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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109 Responses

  1. 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.

    • 3 days straight no sleep I guess give it a few more days

  2. 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.


  3. 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!


  4. 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


  5. 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.

  6. 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.

  7. 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.

  8. 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.



  9. 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.



  10. 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 where you can ask other people about your situation.



  11. 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.

  12. 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.

  13. 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.

  14. Has anyone had issues with insomnia and being constipated. I started taking Phentermine 37.5 on wed and by Friday of the same wk I’ve noticed I’m constipaed I’m drinking enough water. I’ve been eating Lots of veggies and fruits. What’s going on? 🙁

    • Hi Rey! Unfortunately constipation is a very common side effect of phentermine. You may be interested in this blog article to read more about how to combat constipation on phentermine. Hope you feel better soon!

  15. My 1st 2 weeks on 37.5 I couldn\’t get enough sleep. Now the lat couple of days I can\’t fall sleep even though I\’m exhausted.

  16. I just started taking 15mg three days ago.. I find that Im still quite hungry throughout the day. Does the medication take time to go into effect or should hunger be subsided immediately? I was on Qysmia but it got too expensive so my dr recommended I try Phentermine. I was never hungry on that and it was only 7.5mg of Phentermine.. so Im a little disappointed.

    • Hi Jami! Some people find that the effects of phentermine need a few days to “build up”, but if after a about a week you’re still not feeling the effects, it may be worthwhile to give your doctor a call. He/she can work with you to adjust your dosage and/or medication to find something that’s more effective for you. Best wishes!

  17. I have been on Phentermine (37.5 mg) for 54 days now. I typically fall asleep ok, but I wake up around 3:30 every morning. The insomnia hasn’t worn off and according to my prescriber, it doesn’t like it will. Is it possible to take it every other day to help me sleep? It’s working well enough that I there are days that I struggle to eat the minimum calories.

    • Hi Aimee! Yes, some people take their phentermine pills every other day. Another option may be to decrease your dose so that it’s not quite as strong and it’s a little easier to sleep through the night. Either way, you should ALWAYS consult with your prescribing physician before adjusting your schedule or dose. Best wishes!

  18. I started taking Phentermine 2 months ago. I skipped a month since I don’t have time to go to the doctor every month but I did go from 198 to 186 in the 1st month. After not taking it for a month I gained 7lbs back 😫

    I have returned to the doctor to stay again but the side effects are worrisome. I go to bed but wake up after a few hours and unable to go back to sleep. My mouth is constantly dry regardless of how much water I consume and I’ve started noticing my back aching more. Not sure if the back ache is associated with the Phentermine or not but I will check with my doctor.

    Good luck everyone

  19. Where do you recommend purchasing the Phen Caps you mention as an alternative?

  20. I’m on my 5th day of taking 37.5MG and I regret choosing to take this medication. Not sure if it’s because it’s such a high dosage but my first day I had 2 anxiety attacks. I’m on antidepressants and I can’t remember the last time I’ve had an anxiety attack. It effected me less than two hours after taking it and I felt as if I was high on drugs and I was VERY irritable. Then day two til now I’ve been nauseated, having to force myself to eat, dry mouth and some stomach pain and I’ve barely slept. When I actually do sleep I don’t feel rested. As if I wasn’t actually sleeping. I know I’m tired because I have head aches from the lack of sleep. No matter how much I try to sleep my brain won’t shut off which is making my anxiety worse. I don’t do well without sleep. I get irritable, depression increases and all I want to do is cry. After reading all these comments knowing I’m not the only one dealing with these side effects I feel a little better but I will be calling my doctor tomorrow.

    • Hi Nissa! Yes, calling your doctor is definitely a good plan. Hope you feel better soon!

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