Why You’re Not Losing Weight With Phentermine

Why You're Not Losing Weight With Phentermine

Phentermine is undoubtedly an extremely effective weight loss medication.

Still, for all of those who experience weight loss success, some are left wondering why they’re not losing weight with phentermine.

While it could be that phentermine has stopped working for you, if you can still feel the effects of appetite suppression and added energy, then it could be for one of these reasons.

1. Eating Too Much

Counting calories can be a pain, but it’s a good way to know how much food you can have at each meal and for each snack.

In addition, it’s also important to weigh your portions as you could be overestimating how much you’re meant to eat of certain foods.

Test how accurate your judgment is by portioning your food as you normally would and then weighing it out afterward.

If you’re consistently serving yourself generous portions, then you could be consuming A LOT more than you think, therefore making losing weight with phentermine more difficult.


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2. Not Eating Enough

Phentermine works by suppressing appetite, but sometimes this effect can be too strong, to the extent that people have zero appetites and can struggle to eat anything all day.

You may think that less food = more weight loss, but as we explain here.

That’s really not the case; there is an ideal amount of calories that you should be eating to successfully lose weight, and getting that balance right is the key to losing weight with phentermine.

If you’re consuming too few calories each day, your body’s reaction is to think that there are lean times ahead, meaning that it will turn your metabolism right down and cling onto any fat that comes its way, i.e., you are less likely to lose weight.

3. Not Getting Enough Sleep

Establishing a healthy diet and becoming more active will help you to shed pounds.

Still, lifestyle factors such as getting enough sleep also play an important part in your ability to lose weight with phentermine.

When we lack sleep, our brains crave unhealthy easy foods, and our hormones tell us that we’re hungry when we’re not.

This is clearly not a recipe for losing weight with phentermine, so make sure to prioritize sleep and get at least 7 hours every night.

4. An Undiagnosed Health Issue

Before prescribing phentermine, your doctor should check that you aren’t suffering from one of the many health issues that can cause weight gain or make it difficult to lose weight.

These health issues can include a vitamin or mineral deficiency, such as anemia, Polycystic Ovary Syndrome (PCOS), diabetes, or an under-active thyroid, among others.

If you haven’t been fully checked for these types of issues and losing weight with phentermine is proving to be difficult, then ask your doctor for a full health check-up, even if just to eliminate these potential reasons.

5. Not Getting Your Vitamins

Deficiencies in vitamins and minerals lead to a sluggish metabolism and slow bodily processes, meaning your body has to work extra hard to process the food you eat.

As a result, losing weight with phentermine is more difficult. So, ensure you get the recommended daily requirements of important weight loss nutrients for better results.

That said, it can be difficult to eat enough of a variety of foods to meet all these requirements, so we recommend Phen Vites, which contain all of these crucial vitamins plus added premium ingredients like 5-HTP to help boost your weight loss potential even more.

6. Too Stressed

Stress can be one of the underlying reasons for weight gain, so it makes sense that it’s something that needs to be addressed to lose weight.

One study found that participants taught stress-management techniques were able to lose significantly more weight than the participants who weren’t taught these techniques, even though their diets and activity levels were the same. 

Reducing stress balances out hormones and allows your body to function better, so you should aim to reduce your stress levels for success in losing weight with phentermine.

Click here for some great ideas on how to manage stress.

7. Not Exercising

Many people rely solely on diet to lose weight, which can be effective to a certain extent, but it’s the combination of diet and exercise that really gets results.

Unless you cannot exercise due to injury, you should get moving every day, even if it’s just walking for half an hour.

If you find it hard to get motivated to exercise, check out these ways to make exercise more fun.

Exercise is a great stress reliever, and adds to your phentermine energy boost, and research into long-term weight loss has consistently found that exercise is the key to losing weight with phentermine for good.


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8. Eating Too Many Empty Calories

Losing weight with phentermine isn’t all about eating less; it’s more about eating better.

And the same is true of your calorie allowance; just because two foods have the same amount of calories does not make them equally good for you.

Furthermore, low-calorie or low-fat options aren’t always the way to go, so try to avoid light, low-fat, or specific diet foods as they often substitute healthy fats or calories for added sugar or salt and can be more processed than the regular foods they aim to replace.

Instead, aim to get the best from your diet by seeking out foods packed with vitamins, minerals, and healthy fats, avoiding anything overly processed and filling up fiber and protein to keep hunger at bay for longer.

You should also watch the calories and sugar you consume in your drinks, as liquid calories can really add up without giving us any value for money as far as goodness goes.

9. Not Drinking Enough Water

Drinking water has so many benefits for those losing weight with phentermine.

Water suppresses your appetite by filling you up without the calories, it helps your body work better and boosts metabolism, maximizes the effects of phentermine, relieves side effects, and it helps you drop water weight.

Make water the ONLY thing you drink, and you’ll be sure to see a reduction in side effects, a healthier you, and improved weight loss results.

And, for an extra weight loss boost, add the ultimate detox, Phen Drink, to water to see even more success.

10. Not Challenging Yourself

If you’re starting from zero, then phentermine will give you a huge burst at first.

Still, too many people continue on automatic pilot and expect to see these great results all throughout their phentermine prescription.

Instead, you should see it as a learning process, where you expect to progress and improve in all aspects of your life, and not just as a means to an end.

So, challenge yourself continuously to eat better and be more active by setting new targets and mini-goals to keep your interest up, and you’ll be sure to enjoy more success losing weight with phentermine.

Could one of these reasons be why you’re not losing weight with phentermine? Let us know by commenting below!

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    1. Hi Ronda! Always check with your doctor and pharmacist before taking any other medicine with phentermine.
      Rachel, phentermine.com

  1. I started the pill 7 days ago and lost 19 lbs. I walk in the morning, and work out in the evening. I eat no bread, rice, and nothing with sugar. I am on Phentermine and a water pill. I have taken other weight loss pills before and nothing gave me results like this. My friend started the same time changed a little and lost only 4 lbs. You have to eat right and exercise.

  2. I’ve been on phen for two days and the energy level is really high from this pill. 37.5 mg my doctor prescribed me. Day 1 I literally worked out for 2 hours straight. Little lightheadedness at first but it wares off. Any pain I have, after taking this pill I feel it no more.. has anyone else experienced this. what’s in this pill?

  3. Hello Phentermine Users;
    For the past year I have been trying to lose weight. I went and saw my Doctor who ran blood tests she checked my thyroid to my sugar levels etc.… everything came back ok. She decided let’s try Phentermine she put me on 3 month supply I have great results in the beginning. I lost 5 pounds after being on the drug for a month. I just weight my self again this week with starting the last supply. I gained back 5 pounds. I have been watching my portions and working out on a regular basis. I don’t understand why I am gaining weight back. Has anyone out there been experiencing any of my issues and what have you done? What has your doctor recommended you do when you doing everything right??

    1. Hi Stephanie! It is normal for weight to fluctuate slightly, even though it can be discouraging when you first step on the scale. Did your weight end-up going down again, or what did your doctor suggest? Best wishes!
      Rachel, phentermine.com

  4. I have been taking phentermine for 6 months have lost a total of 6lbs. I sleep for 3 to 4 hours a night on work days. Weekends 6 to 7 hours. I don’t eat meat but do eat fish. Have not drank soda in 10 years but still have coffee. I can not stop drinking coffee get massive headaches. Is it a combination of lack of sleep and coffee causing no weight loss?

    1. Hi Tee, thanks for sharing your experience with us. Lack of sleep can contribute to slower weight loss, but it sounds like phentermine isn’t having its desired effect for you. We’d recommend talking to your prescribing doctor about the slow weight loss. He or she is best able to assess your health and consider whether adjusting your dose or trying another weight loss medication could potentially help you lose weight faster. Best wishes!
      Rachel, phentermine.com

  5. Also— would be nice if this thread started with he most recent (current) post instead of one that is from yeas ago. ?

    1. Hi Amanda, this is a great suggestion – thank you! I will pass it along to our IT department 🙂
      Rachel, phentermine.com

  6. I started Phentremine capsules 15mg in Mid Feb. I started out at 248lbs at 5’6”. The first month I was extremely tired. (I also take topamax for chronic migraines so I had already cut out sodas for over 6 months). I assume I was really tired because I completely cut out all processed sugars and fast foods which put my body into withdraw. I still never got the boost of energy 2 1/2 months into take Phen. At my 1st weigh in, one month after being in Phen I weighed 235lbs. I lost about 13lbs. I also was not eating very well, meaning I was forgetting to eat and having tonforce my self to eat the first month. I ended up deciding to buy equate meal replacement shakes because my body was telling me, “ hey you’re hungry” by me starting to get a little confused or cranky. This way I would remember to A) drink a shake and b) you need to prepare a snack for later so you eat real food. The second month weigh in I weighed in at 226lbs. I was a little depressed. My target goal was 220lbs. However, it’s my own fault. I know I would’ve had better results if I had exercised. I did not exercise at all. As in maybe I burned 300 calories a day. I know I need to work on my exercising habits but the second month I was really focused on making healthier eating habits/choices and over coming cravings. Today I weighed myself on a different scale and it appears I have gone up 2 lbs. Which it has been 2 weeks since I did my last official weigh in. I have been more active and exercising more but my appetite isn’t really suppressed anymore. I don’t over eat but I am eating more than just 2 shakes a snack and dinner. I’ll have one shake in the morning and want a lunch and dinner and a snack after dinner. I have a feeling that my body is getting use to the appetite suppressant. That is really all I wanted the Phen for was for my appetite to be suppressed so I could retrain myself not to over indulge. I do fee that so far I am a lot more conscious about what I eat, how much of what I am eating, and I am able to say no to bad choices without giving in to temptation. If I walk away with with being 227lbs but with the will power and confidence that food doesn’t control me or emotions doesn’t control my eating habitats then Phen did what I ultimately needed it do.

  7. I was on 15 mg per day for three weeks, not one ounce came off. My doctor then prescribe 30 mg per day and I’ve done that now for a week and not one ounce has come off. I spend up to six hours per day as a professional housekeeper, I ride a horse twice a week, and do stretching and toning exercises in the morning. I take in about 1400 to 1500 cal per day which my doctor approved. I am on a ton of medication for thyroid, insulin resistance, high blood pressure, pain, neuropathy, it’s Cetera at Cetera. Not to mention I drink a Ton of water every day, And to get an average of seven hours of sleep per night. Why on earth is this medication not working for me?

    1. Oh I am also on anti-depression and anti-anxiety medication Effexor.I went from 147 to 160 while on this medication. I am now holding at 158 pounds and it’s nerve-racking because I can’t seem to break this !

    2. Dear Michelle,

      This is a question best asked to your prescribing doctor or a weight loss specialist. Thyroid conditions can greatly impact the weight loss process, and the amount of medication you are taking could be having additional effects, although no contraindication seems obvious at a glance.

      You -are- doing everything you should be doing. The medication is not working for you. You will need to consult with a professional to find any underlying causes for this.



  8. Help!! I was prescribed 37.5 Phentermine not generic. I have not experienced any burst of energy, no appetite suppressant!! Am I not taking the right medication!! What do you recommend? My pills say K25!

    1. Hi Paula!

      Have you consulted with your prescribing doctor? The only difference between generic phentermine and brand names are subtle differences, like additional flavoring, release method (longer or shorter times for body to process the drug, etc). IF you DO NOT feel the effects of the treatment, we urge you to contact your doctor for further assistance, as we are not qualified to give medical assessment.



  9. I am on Phentermine as well, and am on week 3. My Doctor will only prescribe it for 3 months and said the normal amount of weight loss is about 2 lbs per week, sometimes more in the beginning. He recommended I use the slimfast diet along with the pills, and to only consume 1500 calories. I went out and bought the Aria scale from Fitbit, so I could know my numbers weekly. I haven’t noticed any weight loss whatsoever. However, I have been sick twice in the past 3 weeks, so I have not been able to workout. For those of you working out daily, and eating properly, if you notice there is no weight loss, please remember that you are still burning calories and losing body fat, but you are gaining muscle weight! Muscle will weigh more than fat! It gets people down when they look at a scale since they see no shift in the number! Don’t let this get to you! I do not like relying on a scale to tell me my weight, only using one now to keep track due to taking the Phentermine. If I feel better after working out and my clothes fit better, then I don’t a scale to tell me an irrelevant number, and make me feel bad about myself. I am going to buy a bicycle this week so I can ride in the morning and evenings, and hope this will help me in my weight loss goals. I hope that you can all develop and maintain healthy habits, that’s will stick with you for the rest of your lives, and hopefully inspire your loved ones as well! Many people around me are on the Keto Diet and love it. I am looking into it, just need the time and patience to cook such specific food! Good luck to everyone!

  10. Sometimes there just is no answer and no hope. I’ve been on phentermine for two months with no progress. I’m spending 10-12 hours per week in the gym- working so hard that it often hurts to walk from sore muscles. I’m following a strict, doctor ordered nutrition plan and forget about a cheat day… I haven’t even had a cheat BITE. I’ve been checked for all medical reasons that the weight is not coming off and there are no answers there, either. My vitamins and minerals are spot on. I am consuming a full gallon of water every day. Still nothing.

    I’m trying to just be happy with the positive life changes I have made, hoping that they mean I’m healthier, even if there is 0% chance of ever losing these pounds.

  11. I have been on this med for 2 months and have lost 15 pounds. I’m 5’3 weighted 145 down to 130. I have so much energy, I started working out 4- 5 times a week for at least 1.5 – 2 hours. I’be been moody and stress over little things.
    I walk a lot and eat less than 1500 calories a day. I had to purposefully increase from 1000 a day per my personal trainer (who have not idea I’m taking this). But I haven’t lost anything in about 2 -3 weeks now. I am not sure if I should continue or not. I would like to lose another 5 pounds and or go from 32% body fat to at least 26%.

  12. Hello everyone
    I started phentermine -Prozac 13 days ago 06.01.2017
    Stop taking Prozac about 3 days ago because I don’t like the way it makes me feel .
    My concern is :
    On jun 01 I weighted 148 at dr’s office
    Jun 02 :144
    Jun 03 :143
    And I have been on the same number 143 ever since
    Is there anything that I’m doing wrong . Why isn’t it working for me

  13. Hi I have a thyroid issue it is hyper active I had radiation iodine done but to no avail my thyroid is still hyper but I keep gaining weight . I started phentermine a month ago and went on a 1360 calorie diet I just came back from the doctor and I gained 3! Pounds I also walk 2.5 miles a day and drink 110 ounces of water a day . What is going on why am I gaining weight. Very frustrated

  14. If you had energy when you first started taking phen then it went away, its more than likely a combination of two things, 1) body adjusting to phen 2) lack of quality sleep. Once I started taking a sleeping aid at night, I noticed that my energy started to return. It was nothing like the first two days but I was no longer feeling like a slow-walking, energyless zombie that could not sleep.

  15. Hi everyone. I have been on adipex for 1 week now. I work out 4 times a week. I work a very hard working job. I am a CNA and I’m drenched in sweat most of my shift. I’m constantly running around, lifting people and working my butt off. For example, today I walked 9miles at work. I’m 21, I weigh 169 starting (with clothes) and I am now 164.4 (with no clothes) I’ve lost about 4 pounds which isn’t horrible but yesterday I weighed myself and I was 163 even (no clothes) I never was a bad eater or “unhealthy”. I just have a curvy body and I carry a lot of weight in my legs and butt so I asked my doctor what I could do to help get these pounds off. I eat about 900-1,000 calories a day by choice. My appetite isn’t gone and I also don’t have any increase in energy. I can take a nap during the day but I don’t. I sleep 7-8 hours a night too. I stopped drinking pop (I wasn’t a big pop drinker in the first place. Maybe 5 cans an entire week MAX) I stopped drinking juice too. I strictly only drink water. I intake about 7-13 bottles of water. My question is how did I gain 1.4 pounds in less than 24 hours.. I did weigh myself right after work (walking 9miles today at work) and I am on my period (but I was on my period yesterday when I weighed 163). I also take Wellbutrin XL. Can I be more bloated today and that’s why I’m 1.4 pounds heavier? I’m getting really depressed with not seeing the number going down but it’s going up. Sorry for my language, but I am working my ass off. I take vitamins every day too. I’m doing everything “right” do you think the 1.4 gain is from being more bloated today? Please help me with advice. I’m feeling like I’m failing when all I’m doing is trying non stop to drop this extra weight off. My wedding is coming up and all I want to do is drop 30 pounds and feel so confident at my wedding. Thank you.

  16. Started about 2 weeks ago. Lost 5.5 lbs first week and only 1.2 the second week. My doctor said I would lose about 2 lbs a week so im feeling a little discouraged. Could i not be losing weight if i feel like i am eating too much protein over 80 grams on some days? I work out 5 hours a week and only eat 1000 calories a day. I drink over my recommended 64 oz of water.

    1. Hi Rosalinda – it sounds like you’re doing great! Remember 2 lbs per week is an average, so with 5.5lbs + 1.2lbs in two weeks, your average weight loss per week is still over 3.3 lbs per week. Above average 🙂
      Rachel, phentermine.com

  17. Hi, I have been on phen 37.5 and have been struggling in month 2. My first month I lost 11 pounds. 7 of water in my first week. I am doing HIIT training and intermittent jogging 10 days on 1 day off since I started March 22nd. I cut out white starch flour potatoes bread etc. I drink 100 oz of water daily and I track with My fitness pal and Fitbit. I burn about 2200 cals a day and stay in 1200-1300 cals a day. My diet is fruit yogurt smoothie with nature bounty protein shake. Tuna with 1tbsp of mayo and relish for lunch. Dinner is lean meat and sweet potatoes with veggies brocilli and or carrots. I have never felt my appetite surpress or extra added energy. I have been earning calories back with exercise and I don’t eat them back. I have a cheat every 2 weeks and total cals are 1500 on those days usually a savory desert. I don’t have any thyroid or pcos issues. I’m 41 yo and 5’1. I sleep great. Even nap sometimes. 6 years ago I was put on topimax and Wellbutrin for season depression. I lost loads of weight. I heard that if patients have used Phen befor it’s difficult the next time around to see progress. Does it work the same way if I had used topimax? Should I ask my doctor to add topimax to Phen? Is it possible that Phen just doesn’t work in some patients at all? I feel 11 pounds is a great loss. I also feel I’ve done a lot of the work for the loss myself. It’s now been 7 weeks and Ive been stuck between 178-175 back and forth. It just doesn’t budge. Im not a stressful person but I am becoming stressed with the issues I’m having. Can someone guide me toward a solution and or suggestion. My doctor told me 2 weeks ago to continue what I am doing. I revisit him end of may. I leaning toward stopping them all together. It’s overwhelming enough being overweight, to see others lose 15- 20 pounds the first month without exercise baffles me as I work my tail off!

    1. Hey Booskie I’ve been on topimax while taking phentermine and the topimax just about took me out!! I was having blood pressure issues and I was very dizzy I even fell a few times.Then I was told I possibly could be having TIA’s so I told my doctor to take me off that.I feel great but I’m heavier now than ever but I’m alive!

  18. I started 37.5mg 2 weeks ago today. I have lost a total of one pound. I have never felt the burst of energy everyone explains. My appetite seems exactly the same but my will power is not letting me eat what I want. Cut out all coffee, tea and sodas for the past 2 weeks. All this and still nothing. Sleep more than enough so that cant be it. Would love some energy. I’m starting to wonder if the pharmacy gave me a placebo. I’m so frustrated. I am on synthroid but my Dr insisted this was OK because all my labs have been normal. Please help!

      1. I’m having the same issue also!! I was on it a few years ago and lost tons of weight and had sooo much energy. It isn’t happening this time around. I’ve been on it 2 months and I’ve losy 2 pounds. I seldom eat bad food and I limit my portions. It makes NO sense.

  19. Two summers ago I took phentramine and Prozac combo for about 3 months. I lost little weight. 3 months ago I started again, I lost 6lbs 1st month. 2nd month lost only 2lbs. So my Dr started me on metformin also, minus Prozac. I haven’t lost a thing this month. I workout 45 to 60 mins 4 or 5xs a week. Cardio and strength. I do eat only around 1200 calories a day. Granted not always healthy but for most part it’s healthy. No soda either. I weigh 145 and would like lose 20 more. Any ideas?