Do You Have Insomnia From Phentermine? Read This!

General Phentermine Questions?
Check out the ultimate guide to phentermine weight loss pills!

As a weight loss medication, phentermine successfully reduces appetite and increases energy levels mainly by increasing the release of key hormones which suppress hunger signals and boost concentration, alertness and the ability to sustain a more active lifestyle. However, as a stimulant,it is common for patients to experience insomnia from phentermine, making it difficult to get to sleep for many people who take this medication. Here we explain why insomnia occurs and what you can do to help minimize this side effect while taking phentermine.

Why Does Phentermine Cause Insomnia?

As phentermine is structurally similar to amphetamine, it has a similar impact on the central nervous system with respect to certain effects. Phentermine, like amphetamine is a psychoactive medication, which means that it crosses the blood-brain barrier to directly impact the central nervous system. There is a particular class of neurotransmitters called catecholamines, which are released when phentermine stimulates the neuron bundles in our brain. These include dopamine, epinephrine (adrenalin) and norepinephrine (noradrenalin). This causes phentermine to produce a significant but temporary improvement in both mental and physical abilities, including a positive impact in perception, mood, consciousness and behavior. It is this enhanced alertness and energy from phentermine which improves ability to concentrate on goals and maintain focus, in addition to being more motivated and able to sustain an active lifestyle.

However, this activity in the central nervous system can lead to difficulty sleeping as the brain finds it hard to ‘switch off’. Throughout the day, phentermine stimulates the brain to be more efficient and alert, increasing energy levels and concentration, but these enhanced levels of alertness can then interfere with your body’s ability to sleep, often despite feelings of tiredness. Some people believe that phentermine may inhibit the release of melatonin, the hormone which is released in accordance with the onset of darkness to bring about sleep, however, this is not thought to be the cause of insomnia from phentermine. Instead, it is more likely that the enhanced alertness which phentermine causes by stimulating the central nervous system inhibits the ability to sleep, despite the release of melatonin.


How to Avoid Insomnia From Phentermine

It is reasonably common for patients taking phentermine to experience insomnia during the first few days of their prescription, but if this side effect continues then you should consult your doctor to enquire about the possibility of a lower dose, or to see if he or she has advice for how you can help to minimize this problem.

Taking phentermine earlier in the day can help to reduce the possibility that you will have trouble sleeping when you go to bed, as the energy-boosting effects should wear off throughout the day. You should also try to expel the excess energy that phentermine gives you by exercising or increasing your daily activity level by taking the opportunity to walk as much as possible, such as, by parking at the far end of the parking lot, always taking the stairs, and going for a stroll during your lunch break. Although exercising increases general energy levels as well as energy levels following activity, exercise also aids sleep as it helps to regulate circadian rhythms and balance out hormones which help you sleep. If possible it is best to do more energetic exercise early in the day, as high-energy exercise causes an influx of adrenalin in the body that may inhibit sleep. However, more relaxing exercise such as yoga or Pilates are suitable for later in the day, especially if followed by a period of relaxation and stretching.

You should also try to disconnect as much as possible in the hours before bedtime with a reduced use of smartphones, computers and televisions. Instead, try relaxing with a bath or by reading a book. Ideally, your bedroom should be for the sole purpose of sleeping without interference from technological devices, and you should also avoid working in your bedroom as this association between work and rest can inhibit sleep by causing stress and hormone imbalances. You should also make sure your bedroom is a comfortable temperature for sleeping and that light from the street or other rooms is kept to a minimum. Lastly, avoid caffeine by refraining from drinking coffee, tea and soda in the hours before you go to bed. If your insomnia continues, you may wish to take something to aid your sleep but you must always consult your doctor before taking anything alongside phentermine, whether it is an over-the-counter remedy or a prescription sleeping medication, as it may cause a harmful drug interaction with additional side effects.

Lastly, if you find phentermine is just too strong of a medication for you, and you can’t manage to find a balance you’re comfortable with, then you may want to consider a weight loss alternative. At, we recommend Phen Caps, the #1 phentermine alternative. Phen Caps mimic the effects of phentermine, meaning they increase energy and suppress appetite and cravings. They contain no actual phentermine, but rather 9 innovative ingredients, and therefore do not have the same effect on your sleep patterns while also having no side effects! Maybe the most notable point, they are non-prescription, so can be bought online easily!

Have you experienced insomnia while taking phentermine? If so please feel free to comment below as we would like to hear if you have any feedback or advice for others with the same problem.


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95 Responses

  1. I had trouble sleeping the first few nights but as I also have medication which induces sleep this was a short lived problem.

    • Great to hear! Keep up the good work with your weight loss!

      • This is the first time I have even took this medication and I can’t fall asleep for the life of me some advise please

  2. I am on day 2 of phentermine and can not sleep. Day 1 wasn’t too bad, I woke up twice with loads of energy and fully rested but tonight I can not sleep. I’m tired, I feel sleepy but I just can’t manage to actually fall asleep. I have high points of energy too. Suddenly I’m no longer sleepy and in the mood to clean or run! Then I’m tired again. Plus I’m starting to feel a bit nauseous.

  3. I agree with taking half only for the first few days to avoid its heavy effect. I learned it from a friend who did the same so I follow.

    • Hi, I was wondering how many days did this work for you (taking 1/2 a pill). I\’ve been on Phentermine for 4 days now at 37.5mg and sleep for max 3 hours and then I\’m up for what feels like an eternity. At what point did you find your body adjusted enough to where you could handle the full dose (3-4 days, a week, longer)?? Thanks,

  4. I just flushed mine i take half at 6am,still cnt sleep,it overpowers my ambien.i need something with zero phentermine.

  5. I\’m into my 3rd month on Phentermine 37.5 and I can\’t sleep. 🙁
    I mentioned it briefly to my doc and she said I should be fine.
    I was taking OTC sleeping pills and they helped but now they don\’t.
    I usually fall asleep for 1-3 hrs and the wake up with this weird achy stretchy feeling in my arms and legs. Then I start thinking and 2 hrs passes. I fall asleep again for a couple hours then wake up again with that same feeling. I average 5 hrs of sleep a night. Ugh. I have to keep this up though because I am 220 pounds and 5\”0, and that\’s after the 12 lbs I\’ve lost! 🙁 I used to run for weight loss but I have been sooooo tired for the last 6 years I don\’t have energy to do anything more than work work full time, cook dinner for my husband, and keep the house clean . I want kids so badly but need to be healthier before that, obviously. Phentermine doesn\’t give me energy like other people but I definitely eat less. Just wish I could sleep 8 hrs again!

    • Hey Andrea, As we explained in our article, ‘Lose Weight In Your Sleep With Phentermine’ –, sleep is really important for good health and for weight loss – without enough sleep everything is a struggle for your body, including losing weight. I think you should talk to your doctor again to explain the trouble you’re having and how it might be a good idea to reduce your dosage or try an alternative such as Phen Caps – – which don’t have the side effect of insomnia. Also, we recommend the natural appetite suppressant and sleep-regulator 5-HTP, which is a key ingredient in Phen Vites, the only multivitamins designed especially for weight loss –
      Good luck and I hope that you can resolve your problem soon,

  6. Its my second day taking the pills and like everyone here I can only get 3 hours of sleep. I tried my very best to fall asleep at 10pm but couldn\’t find it until 3am. I then for some reason wakes up at 5 am and fall back to sleep at 6am and wakes up at 8am. I feel I am very tired and want to rest but can\’t. What I like about it though is I dont have the headache that usually follows whenever I lack sleep. Hopefully it gets better for me I really need to lose weight to get rid of all my maintenance medication.

  7. I am now on my 4th day of taking phentermine, from day 1 I have had problems sleeping through the nigh.
    Getting to sleep and feeling ready to sleep is not the problem, as soon as my head hits the pillow im asleep as I usually do.
    But now after approx 3 hours I\’m awake, I still feel tired and want to sleep more, but just cannot get back to sleep properly.
    What can I do ?

  8. Also I\’ve only lost 1lb in 4 days, I\’ve always tired to eat somewhat healthy, So is this pill even working for me, in the right way.

    • Hi Charlie,
      If you feel added energy or less appetite then the phentermine is working. If you tried to eat healthily before, and especially if you’ve always drunk water then you won’t experience the drastic losses that many experience in their first week or two as most of that is water. A pound is still a good amount of weight to lose in 4 days, or even in a week so you shouldn’t see this as a failure. If you’re working out too then a pound lost could mean you’ve lost 3 pounds of fat and gained two pounds of muscle. Try not to dwell too much on the scale – the way you feel, how clothes fit and measuring can help give you a better idea of what’s really happening in your body.

      As for the insomnia, I would suggest that you try taking your phentermine earlier. If you already take it first thing then perhaps you could reduce your dosage to half a tablet for the first few days while you get used to it. Lastly, 5-HTP is a supplement which regulates sleeping patterns and also helps to boost phentermine, so it could help increase weight loss and also help with the insomnia.

      Hope that helps!

  9. Thanks Sally for your feedback,
    I must add that I’m not heavily over weightand nor is my BMI over 30,
    I’m actually only doing this to lose afew very stubborn kilos, that I can’t seem to lose eventhough I’ve been eating healthy for quite a while….
    I have not yet started to do some exercise as i’m tired to during the day since the interrupted sleep pattern.
    I’m just abit worried that this Phen is actually doing more bad than good for me.
    I’m 58 kilos and 5.1 feet in height….
    Is a dry mouth, fatique bad side effects ? 5 day on this is how im feeling.
    I will reduce the dose aswell.

    • Hey Charlie,
      That could explain it as the last bit of weight is often the hardest to lose, even with help. As for the exercise, it sounds counter-intuitive but exercise actually helps to boost energy levels and also helps us sleep better. Maybe try going for a walk to clear your head and also get some fresh air and exercise. Dry mouth and fatigue are other common side effects of phentermine – this article explains more about how to reduce them: Hope you feel better soon!

  10. Im 19 years old and have gained 25lbs within only a few months my doctor agreed this was abnormal for my age but seeing as I am working two jobs paying my own bills and supporting myself she could see where it would\’ve came from. So she prescribed phentermine. I\’m only on day two. Now I\’ve always had trouble sleeping but last night I didn\’t sleep at all I laid in bed staring out the window all night. Today I decided to only take half of my recommended dosage. Luckily by taking the pill I have the energy to get through the day. I really hope this goes away soon.

  11. I been taking the pills for 2 days and I cant sleep at nite

    • Hi Karla, we’re sorry to hear that – what is your dosage? Some people find it beneficial in the first few days to just take half a pill, and then when they become more used to the medication they can then increase to a whole one per day. This article has some other tips about how to get better sleep on phentermine:

  12. i recently just started my 2nd 90 day go around with phentermine and for some reason it feels different. I have always gotten dry mouth from this drug and headaches if i dont eat, but the insomnia has gotten worse. there would be times i would only get an hour of sleep or none at all. Is it possible because of my laid-back work environment, or my inconsistency in taking it? im not good with remembering to take pills because of my fast paced lifestyle. I\’m taking the same dosage, which i know its not that because my first 90 days were pretty smooth with minor insomnia the first week or 2. Should I just be patient since i just started taking it a week ago? Any suggestions?

    • Hi Olivia,
      It’s strange that it’s giving you worse side effects after you’ve already been taking it, but it may be a different manufacturer this time perhaps. We would advise you to take it as early in the day as you can so you have more time to expel the energy before you go to bed. Many people who experience insomnia at the start find it helpful to break their pill and just take half while their body gets used to the side effects, so you could also try that. If half a pill is too weak or your insomnia continues then I would speak to my doctor and see if there is anything he or she could do for you.


  13. Hey im on day 2 i cant get no sleep at all. Im also so hyper! I cannot exercise. I work two jobs and go to school. I have no time. I also did not get a prescription. I just bought it off amazon and the dosage is two pills per day. Do you have any suggestion for me?

    • Hi Shantell,
      Phentermine is prescription only so what you’re taking isn’t phentermine. However, it seems that the side effects are similar so I would say that as the dosage is two per day, you could try just taking one per day and see if the insomnia subsides. Also, try to take the pill as early as possible so that you can expel the energy during the day and by the time you go to bed your body should be ready to sleep.

  14. HELLO,

  15. I took my 1st dose of 15 mg two days ago. At 8 AM, ate a banana with it.

    Forgot to eat the whole day, drank ice tea and water, just did not feel hungry. Began to feel a little weak toward bedtime, so had a plate of vegetables. Did not sleep all night. Did chores and read, never felt sleepy.

    Next day, did NOT take another dose. Did not feel hungry and really wanted to sleep that night. Worked all day (sedentary job). Felt fine, a little forgetful. Did make sure to eat small snacks thru the day. Bedtime, same thing as before, but very very tired. Finally took half a mg of alprazolam and was able to sleep a few hours.

    So, bottom line is I took one dose, had only 4 hours sleep in two days.
    Is this side effect going to improve?

    How often should I take Phentermine? I still feel no hunger, here on day 3. I like that!

    • Hi Kamden,
      Many people who experience phentermine side effects like insomnia very strongly at first find it helpful to reduce their dosage to half a tablet per day as their body gets used to the symptoms and then they find they can work up to a whole pill within a week or so. As for the no hunger, you should always eat at least 1200 calories per day so that your metabolism doesn’t start to slow down and then work against you once you start eating more.
      Sally, phentermine. com

  16. Is it safe/ok to take Melatonin with Phentermine?

    • Hi Laura,
      If you have insomnia with phentermine, melatonin is unlikely to help; your body is still producing melatonin, which is why you feel ready for sleep, but your body is unable to as you can’t switch off. Instead of meatonin, we would advise you to take a natural sleep regulator called 5-HTP. Here is a link to find out more about 5-HTP and how it can help to minimize phentermine side effects and also maximize phentermine weight loss:

      Hope that helps!

  17. Hi,
    I\’ve been on phentermine right at 2 months now. I take 37.5 about 10am every morning. I\’ve lost 26lbs, and for the last 2wks nothing. And now I can\’t sleep. I\’ve tried nyquil, zquil didn\’t work a flip. The nyquil worked for a time. And the last 2 nights I took 2 advil pm. Nothing. I\’ve always been really susceptible to meds, so it\’s surprising to me that I don\’t feel anything at all when taking something to see if it will help me sleep. I just read the comment above. I have taken the 5-HTP several years ago. It worked so well back then that byu the third night I was having a hard time waking up in the morning. I didn\’t even think about it. I\’ll give that a try.


  18. Hi, I know results can vary, but is there a ballpark of how many pounds you can lose from phentermine?reason I\’m asking is because I started taking this 3 days ago and I have no appetite at all although I have drank one large homemade fruit smoothie at home per day and 3 bottles of water. I\’m trying my to force myself to eat but just don\’t have the appetite besides the serious insomnia and gitters I e been having since I started taking these 3 days ago. I\’m 5\’9 & 165 pound I don\’t exercise my target goal weight is 147, based on your experience in how long do you think I can achieve this?

    • Hi Tammy,
      It sounds like your dosage is too strong for you if you have no appetite at all – a smoothie and some water is NOT enough to sustain you! You should talk to your doctor about halving your dose, which is easy if it’s a pill as you can just break it in half. The side effects should also subside if you halve the dosage so you’ll feel better and be able to sleep. You don’t have much to lose and you’re certainly not obese so it’s surprising that your doctor put you on phentermine. But, as you don’t exercise it could be that your weight is hiding the fact that you have a body fat percentage which is higher than it should be. Rather than losing weight you have to focus on making your body more efficient, meaning a faster metabolism and more lean muscle – this article explains why you need to build muscle to lose the fat you really need to focus on losing:

  19. I just started phentermine 37.5 but Im starting off with half. I took half yesterday morning about 10am I took a htp5 the night before I’m still up I layer down last night but was tossing n turning all night I didn’t take a pill today though because I want to sleep tonight if I get sleep I will start my dose again tomorrow at a earlier time.. Can you please tell me how I should do this htp5 with dose or at night before bed?? I wasn’t hungry at all yesterday but in the evening I felt the urge to eat a meal but didn’t today I cooked and ate but half the portion I would usually eat.. Please give me as much advice u can.. I weigh 263 my goal is 180 I still want to keep my butt and a lil thickness 😉

    • Hi Stephanie,
      You should take the phentermine as early as possible in the morning and the 5-HTP is best in the morning too. 5-HTP isn’t a sleeping pill, so you shouldn’t take it before bed – it’s more effective if you take it earlier, especially as you are taking phentermine too. With phentermine you should still get hungry, but just to a normal level, where you are satisfied with the calorie limit you have been given, but still able to eat around that amount each day, usually about 1200 – 1600 depending on your activity level and start weight.

      • Thank you

      • Can I take meclizine 25 mg with phentermine and 5htp?? I tried looking it up but no luck

      • Can I take meclizine with phen n 5htp

  20. I have had great wt. loss results with phentermine. I have the 37.5 mg and cut it into sometimes less than 1/4\’s, take as soon as I arise, 7 ish, workout and walk every day.
    Have an active lifestyle and a very good diet, go to sleep immediately at 1030 ish and wake up 2 hrs later, then I have restless legs !! I have difficulty getting back to sleep and sleep less than an hour at a time till I get up. Am I that sensitive to the drug that the 8 or 9 mgs I take causes me insomnia ?
    I am 63 and very healthy but so prone to gaining weight, I need the phentermine.

    • I\’m getting RLS really bad now too. 3rd day taking 37 and I\’ve slept a total of 3 hours. My legs and arms feel restless 🙁

  21. This is my 3rd night and I literally have slept a max of 3 hours. I\’m so tired I start to doze but then I wake back up suddenly.

  22. I’ve been on the medication for 4 days. I did only take half the first three nights, but sleeping is still an issue. I’m so tired during the day, but when I get home I feel sleepy, but am unsuccessful. I am active. I participate in a boot camp early in the morning before I go to work, but I’m guessing I will have to do more to wear out the meds. The dry mouth is a killer, but still bearable. I stick to 1200 calories a day- or at least try to because I have no appetite. I’m only trying this until the end of the year. 20lbs is my goal. But unfortunately if I can’t get rest I may have to seek an alternative.

  23. I have been on Phentermine for 5 months and yes, insomnia is with me, every night. I\’m going to try the 5 htp idea. I have lost 35 pounds and while I do have dry mouth, keep sugar free hard candies with me. Good luck to everyone!

  24. Hi,
    I have Endometriosis, so it makes it even harder to lose weight due to the added hormones I have in me from this. My DR put me on Phentermine in 2011, and I did exceptionally well on it! Had tons of energy, and no trouble sleeping that I can recall. I was already very active on the weekends, so I chose not to take the pill on Saturday and Sunday. And if I forgot to take it early in the day, I would then take a half.
    I lost 50 lbs from it. However my mom passed away suddenly this year and I gained all of it back plus some 🙁
    My new DR I saw last week prescribed me Phentermine again since I already have taken it. It helps me focus and not feel tired at all! I began taking it Saturday, and had no problem sleeping. However, Sunday night, Monday night, and Tuesday night I have had the worse time falling asleep. I go to bed between 11 and 12 so I get 8 hours of sleep a night, but I maybe fall asleep for an hour, and then back to sleep and then it\’s 3am. I toss and turn and then it\’s 630am. ANd then there\’s more tossing and turning until I have to get up at 8am. I take my pill before 9am every morning. I am going to try taking only a half a pill tomorrow and see if that helps.
    Will I notice a difference taking a half a pill right a way? Or is this something that has to be in my system for a few days to take effect regarding my sleeping pattern?

    • Hi Amanda,
      It could be a good idea to take just half for a couple of days and see how you go with sleeping on that and then increase it back up to a whole pill if your sleeping improves. And, it’s best to take it as early as possible so maybe you could try taking it at 8am when you wake up. Although phentermine can stay in the system for up to 72 hours, the actual effects don’t last that long so you should be able to sleep without problems if you haven’t taken it that day.

  25. This is my second day of taking phentermine, and unlike most people here, I am not super alert all day. After about 3-4 hours of taking it I get super tired! I took about an hour nap and was fine after that. I have had the insomnia, woke up about 7 times in just a 4-5 hour span. Luckily I am a stay at home mom. How long does the insomnia last? I\’m hoping it\’s just while my body is adjusting to it.

    Thank you in advance, looking forward to hearing back.

    • Hi Tess,
      A lot more of our users are reporting this tiredness and fatigue as a result of phentermine, which is strange for a stimulant but not unheard of. To help your body adjust so that phentermine can do the best for you, many users recommend taking a half dosage for the first few days until your body gets used to it. You should sleep better and then feel more energized as a result.
      Hope that helps!

  26. Hello I am on phentermine 37.5 and I just started it three days ago…I don’t have a hard time getting to sleep but I have a hard time staying asleep… my concern is when I wake up I feel hungry and this has been between the hours of 1am until around 3am.. I don’t want to get in the habit of snacking this late but I’m so hungry.. Do you think if I should eat something in between those hours..maybe some fruit or something..

    • Hi Britt,
      I think before you start snacking during these hours, it could be a good idea to look at what you’re eating during your normal waking hours – are you eating enough? Are you eating foods with protein and fiber to keep you full for longer? Remember that you need to eat 1200 calories per day at the very least, and the best way to stop hunger is to be sure to eat every 3-4 hours, aiming for small meals and snacks to keep your metabolism going and your blood sugar even.

  27. I came onto this site by googleing insomnia due to phentermine. As everyone said “i can’t/don’t sleep” this was my second day on phentermine and i all i saw was the clock ticking. Last night i did take ambien and it helped. Is ambian ok with phentermine? I actually feel better during the day but do get an appetite around 9pm.

    • Hi Fay,
      A lack of sleep can affect appetite, so this might be the reason that you get hungry around 9pm. If the ambien is working for you and phentermine is still working too then we would say that it’s ok to take both, although it could be a good idea to double check with your doctor to make sure. If you feel hungry at night then a small healthy snack is fine – the rules about not eating after a certain time of day have generally been found to have no basis in fact, so as long as you keep it light and healthy, eating late is nothing bad.

  28. I’ve just been prescribed this medication. Not for weight loss, I’ve lost 20lbs in two months with simple healthy diet and exercise, but to help with energy and mood during the time each month I struggle with severe PMDD. I’ve been nervous about trying this med, but due to me being very sensitive to most other medications we are running out of treatment options.
    Anyway, Day 1, going into 2. Its 2am and I just woke after only 3hrs of sleep. Thanks for the info and comments. Hopefully this effect gets better for me soon since taking it yesterday took me from feeling borderline suicidal and numb to energetic and only feeling slightly depressed. Long as I can handle the side effects…maybe it will help.

    • Thanks for commenting Cathy – we weren’t aware that people were prescribed phentermine for anything other than weight loss so it’s interesting to hear your story. Hopefully you will start to respond better to it over the next few days.

  29. This is Day 2 for me. It is 4 am and I am up reading these testimonies. I went to sleep around 10:30 pm and woke up 2 am. I have done everything from reading to playing a game on my cell phone, which always assist me in falling asleep. However, that did not help. I checked my heart rate, by cell phone app, and it said my heart rate was 94 at the resting stage. Is this normal? I am very scared of medication and side effects. I am a law enforcement officer and need rest, however, I have to lose 50 lbs. I am going to try to take half a pill at 6 am this morning. I really hope this help me get some sleep at night or do I need to get off this medication all together.

  30. I’ve been taking Phentermine for over three weeks. The first few days, I had terrible insomnia. It got better but for the last 4 nights, I haven’t gotten more than 3-4 hours sleep total per night. I will take half for the next few days and see if that helps. If it doesn’t, I’ll need to try something else which is a shame because it really has helped reduce my appetite. I’ve lost about 8 lbs since I’ve been on it.

  31. I started Phentermine and took half a 37.5mg tablet in the morning for five consecutive days. I had severe insomnia no more than 4-5 hours a night for 5 nights. I also started losing my patience and getting angry really out of character for me – it was awful and damaging to family relationships. Now 6 weeks later I took a tablet as i had a really poor sleep and needed the energy to get through the day. Its now 4am and I can’t sleep!
    I wonder, why make a stimulant-type of medication that has such a long half life. No wonder people can’t sleep! I have previously taken Clobenzorex (Asenlix, Dinintel, Finedal, Rexigen) and it worked a treat – appetite almost non-existent, energetic during the day, and able to sleep at night no problems. Unfortunately it recently became unavailable where I live. Oh I miss it. I lost 3kgs in 6 weeks without a second thought, it was so easy and I slept soundly through the night. The halflife of Clobenzorex is 1-17 hours, half life of Phentermine is 19-24 hours.

  32. I started taking Phentermine 37.5 mg yesterday. I too had insomnia; I always sleep 8 hours but last night I got at most 2-3 hours. In the one day of taking this medication I really saw the difference with eating. I had no cravings, no emotional, or stress eating. I was focused and disciplined. I had previously lost 100 pounds but gained 50. I hadn’t been able to eat 1200 calories in a day in a really long time. I want to keep taking this medicine. I emailed my doctor and she recommended taking it first thing in the morning. For insomnia she recommended an OTC pill called Chlortimetron 4 mg 1-2 at bedtime. I will try that tonight if I have insomnia.

    • Follow up….Today is day 6. I’ve been able to sleep with the OTC med the first few days. Taking medicine first thing in the morning and able to sleep without medicine. I’ve lost 7 pounds!

  33. I’ve been taking phentermine for a month now and as my sleep patterns have altered it wasn’t anything major until 2 days ago. I’ve been up for two days straight. I’m still not tired and have noticed that my appetite is returning. Why the sudden change after a month?

    • Hi Tina,
      It’s difficult to say why you have suddenly started to experience insomnia after a month of taking phentermine, but it could be related to how your body is metabolizing the drug. In general, your body starts off being very effected by the side effects, but once it gets used to the stimulant effects you will gradually see a reduction in side effects like insomnia and jitteriness. However, in the same way that phentermine can make some people more tired, as we explain here –, for other people the side effects can come later or not at all. The hunger may be related to your lack of sleep, as sleep regulates hunger hormones to help us know when we’re hungry and when we’re full. Perhaps you could try taking a lower dosage and seeing if you can start to get back into a good sleeping routine and then work your way up again to get the full benefits.
      Hope that helps!

  34. Hello,
    It’s my first time using this, and after two days in only 3 hours sleep I needed today off the drug. Still feel like it’s in me, still energized and limited appetite. I’m 165cm and weigh 70kgs, I’ve recently gained 10kgs very quickly so my DR put me on phentermine 15mg, could it be too strong for me?
    Could I try taking every second day and still get results?
    Thank you

    • Hi Anna,
      At your weight and height you are only just in the overweight BMI category, so while we think it would be good for your health to lose weight, we think that your doctor might have been too hasty in prescribing you phentermine. It’s an aggressive medication and it sounds like it’s affecting you a lot, so we think it’s probably too strong for you, even at this low dosage. You could try taking it every other day and see if that works for you, although that does mean that on the days you take it you will still get these strong side effects. Therefore, it could be a better idea to speak to your doctor to see if there is anything he or she could suggest.

  35. I’m really struggling with this. Even taking valium or codine doesn’t help. I’m up most of the night, perhaps getting only 2 or 3 hrs sleep. 5th day in and I feel like a bit of a zombie with my brain feeling quite active but my body really suffering.

  36. I am only on half a dose and I can’t sleep-even with 10mg melatonin on board. I am thinking I may have to discontinue. I can’t function on 3 hrs of sleep a night!

    • Hi Lauri,
      As we explain in the article, melatonin won’t help you to overcome the stimulant effects of phentermine. You would be better off taking steps to relax at least an hour before bedtime – including switching off the TV, your phone etc and relaxing with a bath or a book to ease you into a relaxing mindset. If you’ve just started the problem is likely to reduce – perhaps you could take the half dosage on alternate days to see if that helps?

  37. My doctor just prescribed me adipex 37.5 – what time of day should I take them & are they going to last until the next day. I work the night shift from 9pm to 7am?

    • Hi Denise,
      You should take your Adipex when you wake up, which I assume would be in the afternoon. That way it will last throughout your night shift and into the next morning. Then it should have worn off enough for you to sleep when you finish your shift and go home. This article, with specific advice for those working the night shift and taking phentermine, should have some useful tips for you:

  38. What if I take capsules and cannot break it in half? I only take and cannot sleep at all. What do I do then?

    • Hi Heather,
      Unfortunately it’s not possible to break capsules in half so you should speak to your doctor. It sounds like phentermine might be too strong for you as 15mg is the lowest dosage at present so you may be advised to take a different type of medication more suitable to you.

  39. I only took phentermine once 5 days ago and still can’t sleep help me

    • Hi Jesse,
      It sounds like you are extremely sensitive to the effects of phentermine. Take steps to relax before bedtime, switch off devices and technology an hour before, avoid eating less than 3 hours before bed, and make sure that your bed and bedroom are comfortable and a good temperature. The effects of phentermine should wear off soon so the insomnia shouldn’t last much longer.

  40. I have been on Adipex for 5 days. I cannot sleep at all. I just lay awake at night. I am 5′ 6″and weigh 167 pounds. I cant function like this. I am also nervous and jittery. I wonder if this medicine is right for me. I tried splitting the pill in half and it did not help with the sleep either. What can I do?

    • Hi Carolyn,
      Most people find that the insomnia does reduce over time. You could try taking a quarter of a pill, which is equivalent to just over 9mg of phentermine, so this low dosage shouldn’t cause insomnia. If it does then wait a few days and try again with the quarter pill. You may just be extremely sensitive to phentermine so it could be that it’s not right for you, but trying out with smaller doses and working up will help you to see if that’s the case or not.

  41. Thanks for the advice. Is it true that you should not drink alcoholic beverages while you are taking Adipex?

    • Hi Carolyn,
      It’s not advisable to drink alcohol while you’re taking phentermine. The main issue is that the combination can be unpredictable – while some people might be fine, comments we’ve received show that some people can have very strong reactions after even a small amount of alcohol. This article explains more, and also you can read the comments to get an idea of some of the experiences people have had when mixing the two:

      • I do not suggest drinking while on phentermine. I️ did and ended up in the ER twice! My heart was beating a million miles an hour and my whole body went numb. This partially had to do with not getting enough food during the day particularly potassium.

  42. I meant is it ok to take tylenol pm while taking adipex?

    • Hello Carolyn. Thank you for reaching out.

      Yes, you can. But when you are prescribed phentermine, it is a good idea to ask the doctor if he or she would recommend any specific medications for conditions like indigestion, headaches, or other pains that you may be prone to, as some may be more suitable than others when taken with phentermine.

      Hope that helps! You are welcome to join our brand new support group so you can connect with other phentermine users, share your experience and get some valuable advice.


  43. This is my second month on phetermine. Last month I took 15mg and was great ! Definitely helped with my appetite and lost 12 lbs ! This month we increased it to 30mg to help with more weight loss. It was fine when I first started the 30mg but the past week I have not been able to fall asleep until like 4am ! Then I have to get up at 6:30a and work an 11 hr day on 2.5 hrs of sleep 🙁 … I have lost another 5lbs since being on the new dosage but can not figure out how to go to sleep. I\’m trying to wait it out cause it is going back to 15mg next month. Any other suggestions?

    • Hello C.D. Thank you for reaching out. It seems like you are best suited for the 15mg pill. If a lower dosage of phentermine is working for you to suppress appetite and add energy and is also helping you to lose weight then this is a good thing, as it means your body is not building up as much of a resistance to the phentermine as it would if you were to take the maximum dosage.Higher dosages have a higher concentration of phentermine HCL, but due to individual differences in the way our bodies metabolize drugs, this does not mean that a higher dosage will be more effective for everyone. With a higher phentermine dosage, both the side effects and desired effects can be too strong for many people. By comparison, although lower dosages of phentermine tend to give patients fewer side effects, they may not always give patients the desired effects of appetite suppression and added energy to a sufficient enough level for them to really change their habits and successfully lose weight.

      Hope that helps! You are welcome to join our brand new support group so you can connect with other phentermine users, share your experience and get some valuable advice.

      Good luck!


  44. I just started taking half a pill 3 days ago and I feel better than I did when I took the whole 37.5mg. And I only take just half in a day. I do not feel hungry. I do not have the headaches as I did with the full mg. But I have noticed that every morning at 2:30 am on the dot I’m awake. I don’t get up out of bed I stay there and I eventually fall back to sleep within 30 to 40 minutes. I do not get the energy levels which is fine cuz I have a workout routine. Also the biggest change for me is when I took the full dose my heart would speed and with only half it hasn’t done that one time. Unless I’m working out. But my question is this what is it always 230 am when I wake up. What’s happening there?

    • Hello Amber,

      Thank you for reaching out. As phentermine is structurally similar to amphetamine, it has a similar impact on the central nervous system with respect to certain effects.

      Taking phentermine earlier in the day can help to reduce the possibility that you will have trouble sleeping when you go to bed, as the energy-boosting effects should wear off throughout the day. You should also avoid caffeine and processed sugar.

      You are welcome to join our Facebook support group and connect with other phentermine users, today!

      Best regards


  45. Day two on 37.5 and have not slept a minute. I\’m not a great sleeper to begin with, so I\’m not surprised after reading here that insomnia is common. Going to try half in the morning (it\’s 4am, so that\’s essentially now) and an ambien tonight to see if that helps, but can\’t keep taking it if I\’m not going to be able to sleep. On a positive note, my energy level during the day has been fantastic, even with no sleep. Haven\’t had much of an appetite either, though I do eat, just less. Good luck to everyone.

  46. Ive been on phentermine for 4 days now. By the second day, i slept 4 hours on and off. The 3rd day i slept approximately 3 hours. I have the doctor tomorrow we will see what happens. I will try the advise posted a bath, no cell phones, etc. Hopefully that helps.

  47. Hello
    I recently started taking phentramine and realized that I\’m restless, I fall asleep fine but can\’t seem to stay asleep. On top of that I usually was a heavy sleeper, didn\’t wake up to soft noises. It know a pin drop can wake me l! I\’m only on day two, and from the comments I read it may or may not go away, so I\’ll wait and see and go from there. I just wanted to know if I was the only one that felt restless instead of having insomnia.

  48. So anyone know if I can take Phernergan (an antihistamine) to try help sleep while on this Phentermine? I\’m on 30mg and can not sleep a wink. During the day I am
    Bull tired even after taking the pill but Come night time I\’m wide awake. However it\’s only been 2 days.

    • Hi Kelly!

      We recommend, whenever you have questions about mixing drugs or possible interactions, to ask your prescribing doctor or primary care physician, for a more complete, accurate (and safe!) assessment.



  49. I take 2 pills a day, this is my second day and I fall asleep but wake up in three hours should I reduce my intake to one pill?

    • Hi Diego!

      Do not auto-medicate or change your dosage WITHOUT consulting your prescribing doctor or primary care physician first! This is extremely important as phentermine is a potent drug that can have many long-lasting repercussions.



  50. I started taking this stuff Sunday, that night I barely got 2 hours of sleep and it\’s 3am now and I got I think maybe 4 hours of sleep. I can\’t stand it I\’m a person who loves to sleep. I have a long day at college and I need at least 8 hours of sleep and when I don\’t get it it really meses with my depression I\’ve spent the last 30 min crying because I can\’t fall back asleep. I\’ve had sleeping problems before I started taking this and I used over the counter Melatonen and I take this stuff still and it\’ has like no effect on me anymore I usually take one but I\’m gone up to taking 2 hoping it would help me sleep but nothing. How long does t take for my body to get adjusted to this shit? I\’m really hoping I\’ll be back to sleeping normal after a week if not sooner. I\’m currently taking 37.5MG a day.

    • Hi Ginny!

      First of all, we highly suggest you consult with your prescribing doctor whenever you have uncomfortable side effects such as the one you’re describing. You might need a change in dosage or just another alternative. Taking phentermine is also risky if you’re already taking medicine for your depression, so please disclose all this information to your prescribing doctor as well.

      We suggest visiting our Facebook group for phentermine users and our forum, where you can ask other people about your situation.



  51. I was prescribed Duromine 30mg yesterday and today is my first day. I took my tablet at 3 am this morning due to the fact that it buggers around with one\’s sleeping pattern. I had a lot of energy and got things done quicker and more efficiently all while not getting hungry for a second. I do follow a low carb diet along with some forced exercise as I am quite bound inside a classroom, office and recording studio, but have to force myself to eat three meals a day. The only feeling that I don\’t like is the \”buzz\”. I was also a little irritated during the day when I hear loud noises, which is unlike me as I am a music teacher and noises really never bother me.
    I have taken my sleeping tablets about an hour ago and it is still not working. My doctor said that my sleeping medication shouldn\’t clash with Duromine. I am taking Dopoquel and Ivedal. Can anyone please let me know if the moodiness will subside eventually and will I feel normal again while taking the drug. I am gonna be on it for 3 months.

  52. I have been on Phentermine for about 4 months and am down close to 60 lbs, not from the phentermine alone, but a very heavy exercise routine. My problem is always sleep. What I do is quit taking it Friday/Saturday and Sunday. I usually catch up on sleep pretty good and then take it for 4 days.

    I went a full 2 months without Phentermine and managed to drop a few pounds and keep my appetite in check. The ticket really is exercise.

    It\’s and effective medication, but don\’t let yourself become sleep deprived. Take breaks from it. I\’m almost at my weight loss goal and will not take this anymore. I can now manage my weight.

    But in the end, the sleep was hell.

  53. Hi. I was wondering if it was okay to take NyQuil along with my adapex? Unsure if that’s safe or not.

    • Hi Caitlin! Cough medicines and similar are on the list of medications to avoid while taking phentermine, so this is probably NOT a good combination. Check with your pharmacist for alternatives that would be safe to take with phentermine.

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