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Phentermine Side Effects: Losing Weight, But Not Feeling Great?

losing weight

We all know that trying to lose weight by exercising and following a healthier diet is beneficial to our health, but even when we’re experiencing success on our weight loss journeys, it’s not uncommon to feel less than your best while you’re on the way to better health. Coping with phentermine side effects, eating healthier, beginning to exercise for what may be the first time ever, and losing weight as a result can all be tough on you and your body. So, far from wanting to dissuade you from continuing your journey, we’re here to offer some explanations as to why you may not be feeling like yourself, and some solutions to help you get back to feeling better on your weight loss journey with phentermine.

Withdrawal Symptoms

Before we even take phentermine and the reactions it causes within the brain and body into consideration, changing your diet from one that is largely made up of highly-addictive processed foods full of sugar, fat and salt, to a healthier, cleaner diet can produce withdrawal symptoms not unlike those experienced by people who give up certain vices like smoking or caffeine. Your liver is more than capable of handling any kinds of foods that you eat so there’s no need to follow a ‘cleanse’ by drinking the cleanse drinks on the market, just getting more vegetables on your plate and less ready-made meals, processed carbs and saturated fats is enough to start making real improvements to your body and its functioning. However, breaking any kind of bad habit is hard, and when it comes to eating it’s likely to have been a well-established habit spanning many years of your life. Your body’s natural reaction is to want more of what it is used to in order to feel like it used to feel, and the outcome is symptoms such as headaches, nausea, cravings and stomach problems. Fortunately these symptoms generally last no more than a few days and will pass once your body becomes more accustomed to eating natural, fewer processed foods.

If you’re yet to begin your phentermine prescription, one suggestion would be to begin eating healthier before you start taking phentermine. That way, you can establish a healthy eating routine and pass through any potential withdrawal symptoms without having to also deal with phentermine side effects at the same time. However, we would recommend that you combine this first stage of healthier eating with Phen Vites, a weight-loss boosting multivitamin, which will ensure that you are not lacking in any crucial vitamins and minerals as you make the transition into eating healthier and losing weight.


The most common side effects of phentermine are similar to those associated with other stimulants, from caffeine to amphetamine, including restlessness and insomnia. Phentermine can lead to insomnia due to the way it excites activity and causes over-stimulation in the central nervous system, which then makes it difficult for the brain to ‘switch off’, often despite feelings of tiredness. Insomnia can obviously be very frustrating and difficult to cope with, particularly as you are likely to need more sleep as a result of dietary changes and undertaking more activity. This then causes you to experience more profound tiredness during the day, which also has the added problem of making you more susceptible to overeating, cravings and losing focus and motivation. The good news is that these symptoms should pass within several days of beginning your phentermine 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. Some suggestions would be to take your phentermine earlier in the day, make sure to expel the additional energy phentermine gives you by adding more activity into your day, and to take time to disconnect in the evening rather than looking at a computer screen or watching television.

losing weight

Fatigue & Lack of Energy

Fatigue can come as a result of insomnia or following a period of over-stimulation, however, adverse effects of phentermine also include drowsiness, fatigue, and reduced energy levels, as discussed on the Phentermine.com support group on Facebook, which can occur alongside or instead of symptoms such as insomnia. These reactions, whereby a stimulant causes fatigue and sleepiness without an energy boost are called paradoxical reactions, which follow a mechanism that is not completely understood even by researchers and medical experts, but are much more common than people realize. One theory 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 passing, as with many phentermine side effects.

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. These 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 loses, such as 5-HTP and vitamin B12.

Dry Mouth

Dry mouth is one of the most common side effects of phentermine, reported as a side effect by 74% of over 1,200 users in a user poll. Rather than just extreme thirst, it can involve soreness of the tongue and throat, ulcers, and sore gums. While maintaining good oral health and constantly drinking water can help to ease the dry mouth side effect and quench what can seem like an insatiable thirst, it doesn’t actually solve the problem, which is a lack of saliva. As a solution to this symptom, we recommend Phen Drink , a soluble powder which is added to drinking water to increase saliva flow and stop the dry mouth side effect. Phen Drink comes in portable, easy-open stick packs which are added to water to give a great flavor while helping sufferers cope with dry mouth. What’s more, Phen Drink also contains ingredients which actually help to boost your weight loss potential by increasing metabolism and suppressing appetite, meaning that with the help of Phen Drink, your eight glasses of water a day will be working even harder to help you succeed on your weight loss journey.

Mood Swings & Depression

In addition to the more physical side effects that occur as a reaction to phentermine, there can also be some psychological side effects. Some of the side effects reported by users in phentermine.com support group on Facebook include sadness and mood swings. The consensus is that, as a stimulant, phentermine stimulates your metabolism and energy levels, but that it also tends to stimulate and magnify your feelings, amplifying your normal reactions to situations into extreme feelings of sadness, anxiety, anger, etc. Activities such as yoga, meditation, or just taking some time to relax can really help with these side effects, as can talking your problems through with people close to you, or interacting with others in a similar situation in the Facebook support group. It’s also important to ensure that you’re eating a balanced diet and benefitting from natural mood-boosters such as oily fish, selenium-rich Brazil nuts, asparagus and eggs. Vitamin deficiencies can also contribute to a low mood, particularly if you’re lacking in vitamin B12 and folate, which can both be found in Phen Vites, alongside many other great weight-loss boosting nutrients.

Despite some of the negative side effects you may experience as a result of taking phentermine and aiming to lead a healthier lifestyle, the health boost you will experience as a result of losing weight and getting healthy is always worth it. But, by making sure you’re getting enough nutrients, taking time out to relax, and establishing a healthy routine with enough time for sleeping, exercising and having fun, you should be able to triumph over these side effects and make your way to weight loss success while feeling great.  However, if you do find that you are unable to manage with the side effects of phentermine or if your doctor decides they’re not suitable for you, then Phen Caps offer a great solution. Phen Caps are a phentermine alternative which help you lose weight by suppressing your appetite and boosting your energy levels, but which don’t have any side effects.

So, how are you feeling? If you’re losing weight but not feeling great, let us know as we’d love to hear from you.

77 thoughts on “Phentermine Side Effects: Losing Weight, But Not Feeling Great?”

  1. Avatar

    Been on Phen for a week without any significant loss, but am more energetic and active. I have hypothyroidism and ptsd. Should I separate my Synthroid dose from my Phen? Also had very intense, physically painful flashback on day 4 of taking the Phen…is that a serious side effect?

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    I started this medication this morning. I have felt nervous all day. It is 5 pm and I took this at 5 this morning and I still feel like I want to jump out of my skin. What can I do to stop this awful feeling?

    1. Sally

      Hi Teresa,
      At the start some people find it better to take half a dosage if that’s possible for you – if you’re taking the tablet form then you can split this is half but if you’re taking capsules then let your doctor know about your side effects and see if he or she can prescribe a smaller dosage to start with. This should reduce the severity of this side effect as your body gets used to the medication.
      Sally, phentermine.com

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    I’ve been taking Phentermine 37.5 mg, twice a day, 5 hours apart, for the better part of a year. Although the only real side effect I see is dry mouth, I’m wondering if my dr has me taking too much, since I haven’t seen anybody else taking it twice a day.

    1. Avatar

      Hello Jamie. Thank you for reaching out.

      We wouldn’t advice you to take 2 pills a day. Although many people think that a higher phentermine dosage will help them to achieve better results and lose weight faster, it’s not as simple as that. 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.

      Please talk to your phentermine doctor about it.

      Hope that helps! Also, 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. Phentermine Official Facebook Support Group

      Rebeca, Phentermine.com

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    Hi Sally! This article is awesome! I was wondering if you have any tips on how to combat anxiety caused by phentermine? I take 37.5mg dose, half at 10am and half at 3pm. The first dose, I get all the good side affects (high concentration, increased happiness) but when I take the second dose, about an hour and half later, if I get any sort of stressor, I get really anxious with a pit in my stomach.

    1. Sally

      Hi Conor,
      Thanks for your feedback! We have an article about anxiety on phentermine planned for the future but in the meantime, you might find it helpful to schedule your half-tablets around 30-60 minutes before food as this can help to minimize side effects from phentermine. With respect to anxiety on phentermine specifically, we would encourage you to take steps to relieve stress using these techniques: How to sleep better while taking Phentermine, which can also help with weight loss too. Other suggested activities are to keep a journal, breathing exercises, exercise, and distracting yourself by reading, listening to the radio or podcasts.
      Hope that helps!
      Sally, phentermine.com

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    Doctor started me on the same thing, I’m supposed to take a whole one at lunch time but I can’t. I tried to take half for a week and half then took a whole one and I swear it about killed me my heart heart dropped down to 58 I was dying of thirst and I even drank 12 bottles of water and two large Powerades. I was so sick I lost 11 pounds in the first two weeks but I cannot handle the mood swings. I also take Xanax for anxiety and ptsd I stopped taking it after the third week it never got easier for me I couldn’t even handle my kids or my patients at work I was very snappy and when I got off work I had to take a nap it took my energy from me I felt like I was someone else.

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    I took a half one b4 I went to bed and I slept good and woke up feeling normal – will it work the same and help me lose weight if I take it right b4 I go to sleep so I don’t have to feel the side effects?

    1. Sally

      Hi Sam,
      Taking phentermine before bed certainly isn’t recommended due to the stimulant effects. It’s surprising you were able to sleep but even still, taking it before bed means that the energy boost and appetite suppressing effects will be strongest while you are asleep so they will be wasted and won’t be as strong when you wake up. Although the side effects can be uncomfortable and difficult, they are a sign that the phentermine is having effect and they do reduce over time. Taking half a pill can help to minimize the side effects at the start bu you should take phentermine first thing in the morning as prescribed.
      Sally, phentermine.com

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    Been off of phentermine for 6 or 7 months, started back on February 25 with 2 low dose then went right back on the 37.5 dose, I never really had many side effects than the usual my prior months taking it. Then today I notice my feet are cold and chilled going up my calf at times, I’m wondering if I started back on the high dose too soon… I really want this symptom to go away before I take anymore

    1. Sally

      Hi Kimmie,
      Cold feet and legs aren’t a typical side effect of phentermine but if this is a concern for you then you should speak to your doctor.
      Sally, phentermine.com

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    I am on day 5 37.5 I take it all at once. I went to my Dr. & asked for something for energy as I work overnights, I also brought up my weight as a problem. I am at my heaviest I have ever been, even though I have had 5 children via c-section. I just had a baby a year ago, and was 140. At the end of my 9 months I was 185. I managed to get down to 170-175 and gained it all back. One year later now I am 195!!! I work 11-7, I literally have had different side effects every day I take it.
    First day: Took at 6:30 Felt like my eyes were huge, like an actual drug addict.. racing heart, jittery.. def felt the energy, no dry mouth yet, wasn’t very hungry. I made a salad hoping I could still eat it, I took 2 bites and I just couldn’t eat it, not because I ‘felt’ full, it was like a mind thing. Hard to explain. Made it though work a little tired by 4 a.m., got off work and went to sleep normally.

    Second day: Took at 9:30; Severe dry mouth by 10 pm.. drank close to 80 ounces of water, constantly in the bathroom, didn’t feel too much energy as I actually fell asleep sitting up at work at 4 am. Went home at 7, went to sleep…

    Day 3: Took at 10:30 (took later hoping it would keep me up later so I didn’t get tired again) again, severe dry mouth, had TONS of energy.. I got off work at 7, and cleaned my house and did a million things until noon, then fell asleep.. less appetite.

    Day 4: Took at 9:45, I had eaten a small portion of dinner around 7, and small snacks here and there after up until 12:15 I was at work and my stomach starting growling, and I felt super super hungry..??? I had eaten dinner, and had blackberries and raspberries.. and a string cheese on the way to work.. then 24 ounces of water, and stomach was still growling at midnight??… also.. SUPER melancholy, for NO reason. I was driving to work at 11, and a song came on, which I have heard maybe one time before, with no ties to the song I started bawling.. I was also very irritable that night. Also 45 min after taking the pill I felt a bad headache on the right hem. of my brain, and in my right eye/eyebrow area.. also, I wear contacts they got SUPER foggy I had to take them out and rinse them with solution 5 times at work that night; I got off work, went home and slept like usual. But did feel tired again kind of..

    Day 5: Took at 9:30… dry mouth by 10. I now keep several bottles of water everywhere, in most common areas that I go to. I prefer room temp water, but at work I use a lot of ice and water. No headache, but I did experience weird jaw things. I yawned like 6 times in a row, and at the end of the yawn its like my jaw wouldn’t close.. hard to explain. I did feel like that one time before on a different medication, I discontinued because I hated that feeling… kind of moody again today, (it’s day 5 as I am typing this).. it’s now 12:30 a.m… stomach growling again, feel super hungry, had 24 ounces of water since pill, one string cheese and some mini rice cakes??? WHY AM I FEELING like I am starving?!?!? Also, the weirdest effect I have had, both my arms from elbow to finger tips feel like I am missing sensitivity. like a numb/tingly feeling, i do not like this feeling at all. I have zero energy I just want to crawl into bed and lay down right now, also.. I feel like a zombie, like kind of high, I did not feel like this before..

    Overall, I have no idea if this is even working as I don’t have a scale, I specifically went to Walmart today to buy one, and won’t you know I left with everything but that. I am honestly scared to weigh myself, because I have not worked out at all, I know horrible.. I am so busy. As mentioned working overnights, I am off at 7 am; get home.. make breakfast for them, situate them, clean house, appointments, run all necessary errands that I need to, then lay down for “bed” around 11 daily. I am up by 5 as either my kids wake me up, or my phone.. I also clean houses on the side and run errands for people, so some days I have that to do as well. I am active, but not in the sense of working out. Between 2 jobs and 5 kids, trying to stay sane, I’m sorry I don’t have time. I know I need to, or I may not get the results I am looking for. I literally have never worked out, with 5 kids and still maintained a decent body, with a good shape. I am eating right though, No more snacks, I was the snack queen and would often indulge in pizza and chips and chocolate, cereals, pasta… I do not eat meat, haven’t since I was little, but I do eat Seafood, I also wear a waist trainer (I started again, and it really does help.. i fluctuate between the snap up one, and also a work-out one that helps you sweat around your back and stomach, I sweat in it just sitting down, it has no heat.. guessing it’s the material..

    I know all that was super long, I am just really discouraged thus far with it, I know people will say it’s far too early to be or to just give up, but why am I starving, and exhausted.. the complete opposite of what I needed this for. ughhhh.

    1. Avatar

      Thank you for putting the time into this comment! I was expriencing a lot of the same symptoms. Such a bummer that this “magic pill” doesn’t work for us.

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    I take 37.5mg phen at 6am. Drink a full glass of water while taking it. Eat on my way to work at 6:30. I am soaked with sweat by 7:30 and stay that way until I get off at 4. (Work in packing house). I have to drink 1-2 gallons of water while at work or I get bad dry mouth and fatigue. I will also feel fatigued if I don’t eat very small amounts of food 5-7 times per day. I get about 2 hours less sleep per night on phen and do have a mild headache fairly often. I have slightly elevated emotions on phen but over all I’ve lost 27lbs in 40 days. I’m looking forward to getting off phen but for losing weight it is great if you eat, drink and exercise correctly.

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    Hey so I’ve been taking Phentermine the pill is white with blue specks and shaped like a football, loved it no side effects besides dry mouth and swollen uvula, headaches! I’m drinking a gallon of water every day!

    Ok so here’s the thing this month I went to a differeny doctor and she prescribed me phentermine but the pill it’s fatter, and round on the edges,still white with blue specks ! So after about a day or 2 taking the pill I’ve been have this problem with extreme dizziness spinning feeling, pressure in my sinus and some nausea, and heartburn! I stopped taking my thyroid supplement thinking it was it! So then I stopped taking the phen for a day and felt a little better the next day too so the third day I took it again and yep that awlful feeling is back :/
    SO MY QUESTION if anyone can help 1: have I been taking the pill too long (yes I’m eating and drinking plenty)
    2: is it the difference in the pills I was prescribed maybe that new one has something different that I’m reacting too??
    PLEASE HELP I loved losing weight and the feeling happy no I’m miserable and sick and yucky

  11. Avatar

    I started taking phen about a week ago. I lost 4lbs in like 5 days which waa great. But I had really really dry mouth and my breath started smelling really bad. How long after you stop phen will it go back to normal. I work with people face to face I can’t afford to have bad breath.

    1. Avatar

      Hi Sara! Unfortunately we don’t have an exact answer for you since side effects vary so much person-to-person. However, most people feel the reactions (including dry mouth) most strongly during the first 1-2 weeks of their prescription, and then experience some improvement soon thereafter. In the meantime, you may be interested in our articles on coping with dry mouth and hydration on phentermine to give you some ideas to deal with the dry mouth. Best wishes!
      Rachel, phentermine.com

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    I. Have been taking this pill for 6 days and lost 15lbs. I am also diabetic and cant seem to make myself eat anything more than a couple of bites of anything and then only twice a day. Any suggestions?

    1. Avatar

      Hi Zoe! We would suggest speaking with your doctor about a dose adjustment. Given your diabetes, it’s extra-important that you eat regularly to maintain a steady blood sugar and avoid lows. So, if your phentermine is totally eliminating your appetite, this is something your doctor should know. If you haven’t already, it may also be worth talking to your doctor about phentermine and diabetes management in a more general sense since significant weight loss can also effect how your body handles insulin and blood sugar. In the meantime, have you tried meal replacement shakes? They make some shakes – like Glucerna – that are specifically formulated for people with diabetes. A shake, or a balanced snack, could help you get some calories (and glucose), even if you aren’t in the mood for a full meal.
      Best wishes!
      Rachel, phentermine.com

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    I took phen for two days. Had very bad stomach cramps.
    Felt like bad gas, is this a side effect and will it continue or lessen with time..? Should I consult my dr,?

    1. Avatar

      Hi Lorrie!

      We do suggest you consult with your doctor whenever you feel uncomfortable by any side effect from the phentermine treatment. Only healthcare professionals are capable of giving you an accurate assessment and response. It might be something as simple as adjusting your dose, or it might require other actions suggested by your prescribing doctor.



  14. Avatar

    Hi, I taken phentermine in the past, like 5yrs ago and I had the shaky feeling, not sleeping, mood swings, etc… Now I am taking adipex not the generic brand. I have been taking it for two days and I’m not having any side effects. Does that mean its not working?

    1. Avatar


      Not at all. Different things, like the dosage, your age, and other factors all influence whether you have side-effects or not. Having or experiencing side-effects is in no way at all a sign of the phentermine actually working on your body. Count yourself lucky!



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    I’m hoping some one has experienced this, or can answer this for me. I’ve been on 37.5mg phentermine for about 2 weeks now. I started at 15mg and titrated up. I feel great on it. A little dry mouth, no jitters, but more energy, no insomnia, nothing bad. EXCEPT. Sometimes… in the evening, I start feeling “sensations” in my arm and neck. My heart rate is always perfectly normal (I check it constantly) but I “feel” like something’s wrong. I think I am just having anxiety about taking the pill because my doctor was really hesitant to prescribe it and I read so many horror stories online. ( I’m trying to become healthier, not harm myself in the long run.) If I have no heart rate/blood pressure issues, no palpitations etc. can I assume everything is ok and I’m just letting anxiety get to me? Like I said, it is only sometimes, like once a week. And literally 12+ hours after I’ve taken it. Otherwise, the effects have only been positive! Thanks in advance for any helpful responses!

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    I’m 39 and had surgical hysterectomy. Can’t go in any hormones. Menopause was sooo bad for me. Weight gain was almost immediate and nothing I did helped. My doc gave me Phen a year ago (just 15mg) and I dropped 20lbs. But better than that… I had the reverse effect – it actually HELPED my hot flashes and night sweats. I stopped it about 6 months ago and within a few weeks the menopause symptoms came back with a vengeance. Restarted Phen (15mg again) and same tho g – hot flashes night sweats are so much better. Also helps that my appetite is curbed bc menopause does a number on that too! Anyone else find it helped menopause??

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    I’ve been taking phentermine for two weeks now and I don’t think my body can handle it. I haven’t been sleeping at all, and for the entire two weeks I’ve been on it, it has made me incredibly nauseous. I feel like I’ve had the flu for two weeks. Is there any reason why this pill would be making me so sick? I take it first thing in the morning with a full glass of water, and I wait two hours to eat.

    Any suggestions? I’m just about ready to throw in the towel.

    1. Avatar

      Hi Tammy! I would definitely recommend that you check with your doctor. It may just be that phentermine doesn’t agree with you, but if you talk with your doctor he/she may be able to adjust the dose or recommend another medication so that you don’t feel so sick. Hope you start feeling better soon!
      Rachel, phentermine.com

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    hi i started phentermine about 5 days ago only side effect other than dry mouth is very bad HOT FLASHES ive gone through menopause and all of this stopped i also was on phen a few yrs ago and didnt have the flashes is this from the phen !!!!

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    Hi I’ve been taking it prescribed by a cardiogist for a few weeks. First few days 1/2 pill I felt pretty amped. Once that calmed down I moved to a full pull. My overall feeling is pure exhaustion. Like…want to fall asleep by 10am. And it lasts most of the day. I’ve read something about adverse reactions like fatigue vs speedy – but does this go away?? And if Its affecting me this way, will it even work?

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