tired on phentermine

Why Am I Tired On Phentermine?

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As well as an appetite-suppressant, phentermine is meant to be a stimulant, giving you extra energy to help motivate you into being more active in your daily life. However, not everyone experiences this energy boost; many phentermine users contact us and use our phentermine forum to explain how they actually feel more tired on phentermine. Here we explain why some people can experience tiredness when taking phentermine, and what can be done to overcome this problem.

Why Am I Tired On Phentermine?

While many people experience a boost of energy, and even side effects such as jitteriness and feeling ‘wired’ while taking phentermine due to its stimulant effects, others can have a very different reaction. Forum posts show phentermine users reporting that they feel sleepy or mentally and physically exhausted while taking phentermine, indicating that it is producing the opposite of the desired energy-boosting effect. So, why exactly are people reporting that a stimulant is making them more tired?

1. Insomnia

As a stimulant, phentermine can sometimes work too well, meaning that users can suffer from insomnia. This side effect leaves them wide awake late into the night, despite taking their phentermine first thing in the morning. So, one logical conclusion as to why those on phentermine report feeling tired would be that the medication has caused an over-stimulation of neurotransmitters, leaving them alert and unable to sleep despite their tiredness.

However, this implies that the patient has experienced this initial burst of energy expected from phentermine, and that their tiredness is more as a result of an inability to sleep due to over-stimulation, rather than as a direct result of the phentermine medication. But, forum posts and blog comments indicate that insomnia is not always the cause of feeling tired on phentermine. In fact, some people have reported that they feel sleepy and need to take several naps per day when taking phentermine, including just after taking it, and others describe feelings of exhaustion despite sleeping well at night, as shown in the comments on this blog article in particular.

2. Paradoxical Reactions

So, there must therefore be another explanation as to why people feel tired on phentermine; namely, paradoxical reactions. It has been well-documented that stimulants can cause people to experience fatigue, drowsiness and reduced energy levels – the very opposite of what would be expected from a stimulant. In addition to more common stimulants such as caffeine, which has been shown to cause this effect, phentermine has shown to leave people feeling drowsy and tired, which can occur alongside or instead of symptoms such as insomnia. These paradoxical reactions, whereby a stimulant causes fatigue and sleepiness without the anticipated energy boost, follow a mechanism that is not completely understood, even by researchers and medical experts, but are much more common than people realize.

One theory to explain this is that, since phentermine stimulates several receptors, including serotonin, it can cause feelings of tiredness and fatigue as serotonin is released as the body’s way of regulating sleep. Alternatively, it may be that the pre-existing balance or imbalance of chemicals in the brain on a particular day are the trigger for what effects the phentermine will have on that particular patient, in the sense that it may correct an imbalance or over-stimulate a certain chemical, leading to somewhat unpredictable reactions. This also indicates that you may not always have this reaction to phentermine and that this side effect may be temporary, as with many phentermine side effects.

tired on phentermine

How To Overcome Tiredness On Phentermine

If you’re feeling drowsy or tired on phentermine then you might want to fight this tiredness by downing coffee, but it’s best to avoid additional stimulants. If you’re in a position to be able to take a short nap, this should give you a much-needed burst of energy to get you motivated for the rest of the day. If you’re at work or too busy for a siesta then these ways to boost energy on phentermine, such as drinking more water, stretching, or going outside for a quick breath of fresh air, should help to keep you going until you can rest.

As with many phentermine side effects, patients usually experience these issues of tiredness most severely at the start of their prescription. So, if you’ve just started taking phentermine and you’re suffering from fatigue or feeling sleepy, then this side effect should pass within the next week or so. While you are experiencing this paradoxical side effect, you may want to reduce your phentermine dosage to see if this helps you to feel more awake and motivated, but in general, getting plenty of weight-loss boosting sleep, lots of water and a variety of healthy fresh foods should help you to feel less tired on phentermine. And, if you feel able to get some exercise, then this will actually help to get your energy levels up, especially if you participate in an energizing and uplifting cardio activity like aerobics or Zumba.

However, if you’re feeling fatigued or lacking in energy while taking phentermine and the problem persists, you should consult your doctor as it may be that you have an undiagnosed medical condition such as thyroid problems or PCOS. It could, however, be something as simple as a vitamin deficiency; for example, low levels of magnesium can cause tiredness, as can insufficient levels of vitamin C. To counteract these problems with fatigue while also ensuring that you are getting the right amount of crucial nutrients, and simultaneously giving yourself a great weight-loss boost, we recommend that you take Phen Vites, the only multivitamin you’ll need if you’re serious about losing weight. Phen Vites contain a multitude of essential vitamins and minerals for good health and more effective weight loss, as well as nutrients specifically given to phentermine users to boost their losses, such as 5-HTP and vitamin B12.

Lastly, if it’s just a case of phentermine not giving you as much energy as you had hoped, then adding the weight loss supplement Phen Caps to your daily phentermine will give you an added boost of energy, as well as helping to curb your appetite too!


Are you feeling tired on phentermine? Let us know by commenting below!


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26 Responses

  1. I Just started and I’m experiencing heavy drowsiness mixed w/ small amt of anxiousness. I also have noted a residual headache starting when I don’t take the nap. Yesterday I combated it by drinking a caffeinated beverage but I’m trying to get away from those drinks to aid weight loss. This is very confusing.

  2. I took Phentermine a couple years ago and it worked great! No side effects, energy levels were super high, weight loss was great etc… This time around after I was done breastfeeding I was put on it and it’s really bad.

    Symptoms include:
    *No weight loss

    I get 8-9 hours of sleep and those are the sleep hours I’ve needed my whole life to feel well rested. I drink AT LEAST 64oz of water, I’ve tried coffee to see if that helps (helped somewhat). I was Dx with Hypothyroidism but it’s in range and I do take my Synthroid as prescribed (this is the only change from when I took it last).

    • Yesenia, I would like to keep in contact with you as are symptoms and DX and the same . Email me tmills183@gmail.com

      • I have the same problems and then some.

    • I take adipex-p 37.5mg and I\’m get sleepy 3-4 hours after I take it. I wonder what could be cause of it.

    • Hi everyone do your pills have a weird C shaped E 16 on them? Then they are from Epic Pharma LLC – Just the name sounds sketchy to me TBH – And I was on Adipex P years ago and it worked wonders for me- I became a marathon runner! Now I just had a baby well not just.. been trying to lose the baby weight for 15 months now with this junk and I\’m so so tired only a few hours after taking this… I\’m talking EXHAUSTED – I work from home and can\’t get out of the bed can\’t get to the gym – this is not me – I\’m convinced there\’s something wrong with it now – I get mine @ Walmart but my insurance is forcing me to switch to CVS so next month I\’m going to ask my doc for adiepx brand – hopefully that is like the old stuff! Keep me updated everyone! Best of luck

  3. I took Phentermine a couple years ago and it worked great! No side effects, energy levels were super high, weight loss was great etc… This time around after I was done breastfeeding I was put on it and it’s really bad.

    Symptoms include:
    *No weight loss

    I get 8-9 hours of sleep and those are the sleep hours I’ve needed my whole life to feel well rested. I drink AT LEAST 64oz of water, I’ve tried coffee to see if that helps (helped somewhat). I was Dx with Hypothyroidism but it’s in range and I do take my Synthroid as prescribed (this is the only change from when I took it last).

  4. I took my first dose of phentermine 37.5 mg today. I was nervous about taking a new medicine and thought it may cause my anxiety to kick in. In fact, the opposite happened. Within 45 mins I was so tired I couldn’t keep my eyes open and I slept about 9 hrs. Straight. I do, however, suffer from hypothyroid like the above post. I am also on synthroid, but I will be getting lab work done soon to make sure my levels are still good, as I have had to up my dosage 5x my thyroid was 15.88 and was supposed to be between 0. And 4. So, mine was off the charts. I do feel like my appetite is gone ,so it is working. I think it might be my thyroid. We will see as soon as labs come back!!

  5. I have been on phentermine 37.5 MG for about 6-7 weeks. I have been tired to the point of being foggy and groggy at work. I have even tried extra water, exercise, sleep and nothing helps me. I have even tried taking it at night so in the morning I would be less drowsy. I take blood pressure medicine, anti-depressants and multi vitamins. I wish it had worked for me but I have been off it for 3 days and I feel way better, so I am going to my doctor tomorrow to let them know.

  6. I just begin phentermine it\’s not even a week. But i\’m so sleepy. I\’m drinking water and tea walking and exercising but nothing help. With this lazy feeling am I still able to lose wait?

    • Hello Erin,

      Thank you for reaching out. We would advice you to avoid caffeine and instead go for protein shakes or green juices to give you a boost of energy during the day.

      Also, take a short nap, this should give you a much-needed burst of energy to get you motivated for the rest of the day.

      If you find phentermine is not something your comfortable taking, there is an alternative available. We recommend one on our website, they are called Phen Caps, they do not contain phentermine and therefor do not need a prescription or have any known side effects.That is always a great alternative and we have had great responses so far. I will leave their website below!


      Hope that helps! You are welcome to join our Facebook support group and connect with other phentermine users, today! https://www.facebook.com/groups/1069871763087734/

      Best regards

      Rebeca, Phentermine.com

  7. Been on phen phen 7-8 days,1rst day I was fine,exercised,walked 8 miles,2nd day I took it I got so tired and udkn why???it cost me $200+ cash c doc just to get 25 pounds off of me!I been taking them everyday THINKN the tiredness will go away but right now I\’m so tired and I did alot of crunches & etc about 35 mins ago..well 35 mins ago I finished them..yes the past few yrs I have had a hard time sleeping at night,I wake up so much threw the night, phen phen I sleep fr 9-7 am??then want to doze off threw the day so I get up and walk,exercise ,protien shake I do DRInk at noon!!yes I have ADHD were trouble concentrating could that be my problem do the pills have ADHD med I\’m it??should I take for another wk to c if affects go away?should I get b12 etc to take? it makes me mad I felt great 1rst day and yes I sleepy everyday after that??idkn my energy at 40 has Ben blah and I go to doc cause I wanted to loose sum weight being a new grandma and I am tired!I will take 4-5 more days to see if it turns around for me,, if not money down drain I could have bought grandson a csrsesr

    • Curious what your doctor said, I also have ADHD and feel so foggy and exhausted like a mattress is on top of me in the morning trying to get out of bed and nearly lethargic the entire day, I have known a lot of people that have taken this and they all run around like they are on speed

  8. I am taking duramine and its the same thing i am usually wide awake and feeling amazing but i had to stop for one week to go to Bali as i would not risk taking them over there and now these symptoms have clicked in massively:( perseverance i have ten more kgs to go ive lost 20 kg so far 🙂

  9. PLEASE HELP. Hi all I started taking phentermine 37.5 about 2 weeks ago and I have only lost 5 pounds. I do not have the same burst of energy that everyone experiences. I am wondering if it is because I take a sleeping pill at night. I would drink a meal replacement shake for breakfast and dinner and have a small salad for lunch. I was hoping to lose a little more weight by now. I am very active at work (I work in a prison). Any suggestions would be great. I take the Gummi b-12 are the injections better? I am 5\’2, 200 lbs 48 years young. Thank you

  10. I have taken phentimine for years. I now am exhausted every day.I can barely hold up. I am 67yes old and own a farm. My energy levels r so low that I can\’t believe it..what has happened?could I be immune to it.

  11. Hi. Female, 62 years old, 5\’1\”, 180lbs. Italian (part of the problem right there .. lol). Out of 8 children I am the skinny one in the family (eeeek). About 3 years ago started feeling sluggish, a year later pretty much quit working and got hooked on Steve Wilkos and Judge Judy. Got to the point to where I put a GPS on my husbands phone so I could keep an eye on him as to when he was coming home from work, so I could jump up 30 minutes before and do the dishes, make the bed, etc. After 4 ER visits for high blood pressure my husband took me to Loma Linda where it was found that my gallbladder has actually poisoned and died in me. From beginning to after surgery gained over 50 lbs. Went to my regular doctor to get a check up and thumbs up for me to go to weight loss physician. First visit. Friday 6/30/17. Started Phentermine 30 mg and B12 with LipoDen Plus. The first two days I was laughing so hard, getting a kick out of the out-of-body experience. It was almost to much energy. Had to make myself eat. Wouldn\’t dare drive my car. My first week I decided to just keep an eye on how it was all going to make me feel. By the end of the week it was perfect. Weighed in following Friday and down 4 lbs. Happy. Second week incorporated walking and cutting my favorite meals in half. Weighed in .. 4 more lbs! Oh yeah! Third week, my husband bought me a stationary bike. Nothing fancy. Additionally, I began my calorie count diary. 3rd Friday check-in down 2 more lbs! 10 lbs. in 3 weeks is great. Going into 4 week and have everything down pat ??. Up to 45 minutes on bike ever day but Fridays and still walk every other day to burn off the rest of the energy. Have never slept better (except the first 2 nights .. ugh).

    • Hi Jeanne! Thanks for your comment and we’re happy to hear you’re doing so well on your phentermine journey! Best of luck going forward!!
      Rachel, phentermine.com

  12. Hello, I am taking phentermine and it makes me Sokol sleepy! Should I just take the pill at night before I go to bed?

    • Hi Brittany, thanks for your comment! It’s usually not recommended to take your phentermine before bed because you want the pill to have its strongest appetite-suppressing effects during the day – when you’re awake and eating. Instead, try to combat the sleepiness by drinking plenty of water, eating enough to fuel your body, and getting some quality sleep at night. Still, if your drowsiness persists, or starts interfering with your daily activities, don’t be shy about double-checking with your prescribing doctor to see if he or she has any ideas!
      Rachel, phentermine.com

  13. I cant believe all these comments. I started 1-1/2 weeks ago15mg. I have not lost any weight despite eating only 3 healthy small meals a day. Im exhausted and this is my 2nd day off work. I never take days off but all I want to do is sleep. I got up and took the pill at 7am and then slept again until lunch despite sleeping all night from 10pm. First few days I was hungry as well. I seem to have none of the benefits of the drug. Im going back to the docs today. Im starting to wonder if I have an undiagnosed thyroid issue. That would explain why I have been unable to lose weight before now despite always being on a diet. Only other side effect Ive had is itchy skin. Why is this happening?

  14. I have been takin Phentermine since June and since about then I am having problems staying awake at the wheel and sometimes at work. It is becoming so bad that it is interfering with life. I have ADHD and am wondering if the Phentermine is having the opposite effect on me. Sometimes I get bursts of energy but not really sure if it is different than before taking the Phentermine. Recently upped the dose and seems to be making this worse.

    • Hi Sarah! We recommend speaking with your doctor about this concern ASAP, especially since it’s interfering with your daily activities. Everyone reacts to medications differently and you may be experiencing an opposite reaction to phentermine (either due to your ADHD or something else) that’s making you so tired. Regardless, your doctor would be the best person to help you understand this reaction and find a solution. Best wishes!
      Rachel, phentermine.com

  15. I have been on Phentermine for almost 3 months now. I have PCOS and insulin resistance . I was an athlete growing up so my weight gain over the years has been very hard. Thankfully my doctor was the one who brought phentermine to tryand help jump start my weightloss. The first month I lost 18 lbs wit my eating healthy, riding my bike, and the meds. I have losta total of 33 lbs. and in the last month, i began feeling very tired and can’t get my rear end out of bed in time to work out before work anymore. I’m having issues with insomnia now and tired all day. In the beginning it was great but now as I’m almost at the end of my 3 month jump start that my doctor put me on, I am worried that it is going to create a bad habbit again and make it difficult to get up and moving to work out in the morning now.

  16. I was diagnosed with hypothyroidism. I have not needed to take Levothyroxine in almost a year since my thyroid has been controlling itself. I have taken Phentermine 37.5 for 3 weeks. I began feeling so tired during 2nd week and continue to feel the same way in week 3. I have even skipped 1-2 days of it because it my appetite was non existent, I could not get out of bed, and felt really dizzy when I did.

  17. When I first take phentermine I have a load of energy. But after a week I get tired. I have to do 1 week on and one week off. I think cause it makes your heart rate fast that it tired your body out after too much use

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