Can You Take Phentermine Long-Term?

Can You Take Phentermine Long Term

While phentermine is very useful and effective in helping you to lose weight, it is important to remember that taking phentermine long-term is not recommended and that phentermine has always been intended for short-term use only.

This is because of how phentermine affects your heart and can cause serious side effects; plus, it can be addictive and becomes less effective over time as your body becomes accustomed to its effects.

Here we explain more about why phentermine is only recommended for limited periods of time, the potential risks of taking phentermine long term, and how you can maintain weight loss without taking phentermine long term.

Why Phentermine Is Recommended For Short-Term Use

Phentermine has been available on prescription since the 1970s for the short-term management of obesity after first receiving FDA approval in 1959.

It is recommended that phentermine only be prescribed short-term, typically interpreted as up to 12 weeks. There are two reasons why phentermine is only prescribed for a short period of time:

How Phentermine Affects The Body

The first reason is because of the effects phentermine has on the body. Phentermine is classified as a controlled substance, recognized as having a structure similar to amphetamine.

Like amphetamine, phentermine acts on the central nervous system to stimulate neurotransmitters in the brain, including dopamine, epinephrine (adrenaline), and nor-epinephrine (nor-adrenaline).

This causes phentermine to increase energy levels, suppress appetite, and minimize cravings, making it an effective weight loss medication that helps you to lose weight quickly.

However, for many patients taking phentermine, the initial effects can be quite aggressive, including feeling ‘wired’ and unable to sleep, with little to no appetite, and a variety of side effects, such as dry mouth, anxiety, depression, nausea, and mood swings.

Over time these side effects reduce, but so do the effects of appetite suppression and energy boosting. This is because the sustained use of many drugs causes adaptation within the body that tends to lessen the drug’s original effects over time, known as drug tolerance.

Many phentermine users experience a reduction in the effectiveness of the medication over time, which indicates that tolerance is occurring within the body until, eventually, patients experience fewer and fewer of the desired effects, with even the maximum dosage of 37.5mg providing very little appetite suppression or extra energy.

This is why it is crucial to take a break from phentermine, and then only take it for a further period if it is deemed necessary by your doctor.

It is not uncommon for patients to take phentermine more than once. However, it is not advisable for patients to take phentermine for several years.

Having to take phentermine many times would indicate that it is not effectively helping the patient to achieve long-term weight loss and so alternative treatment should be considered, such as counseling or more personalized dietary and lifestyle advice.

As a stimulant, phentermine also causes the heart to work faster as a means to enable the body to work more efficiently at processing food into energy.

Over time, this can put stress on the heart, resulting in symptoms such as chest pains and an increase in blood pressure, among other heart-related side effects.

Therefore, due to an increased risk of harm to the body coupled with a reduction in effectiveness, taking phentermine long-term is not worth the risk to the patient.

The Limitations Of Phentermine Research & Development

The second reason that phentermine is only recommended for short-term use is that the drug was never systematically tested for long-term use and, therefore, cannot be considered safe when taken for longer periods of time.

In the research and development stage, including clinical trials where patients took phentermine and were observed for weight loss and side effects, phentermine was only ever tested for short periods of time.

Therefore, the recommendation for it to be taken up to 12 weeks is based on the length of time participants in these clinical trials took phentermine. 


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Because phentermine was first tested in the 1950s, it was not subjected to the rigorous testing methods that the FDA now imposes, as shown by the extensive year-long trials into Contrave, the latest weight loss drug to be approved by the FDA.

Therefore, when considering the possible long-term effects of taking phentermine, we have to rely on anecdotal reports from individuals and infer results from the long-term effects of taking drugs with similar substances to phentermine, such as amphetamines.

The Risks Of Taking Phentermine Long-Term

As we have explained, phentermine is not intended for long-term use, but despite this, there are still many posts in our Facebook support group from members who have taken phentermine for several years.

Conversations about taking phentermine for extended periods include reports of migraines, heart problems, high blood pressure.

In particular, one user is taking phentermine after nearly 7 years, despite having a BMI of 22, and is now experiencing eyesight problems as a result.

The fact that this user is a healthy weight would indicate that this member has developed a dependence or possibly an addiction to phentermine, whereby she no longer needs to lose weight but is still taking phentermine after years, and now her health is suffering.

Other conversations that discuss addiction to phentermine include people talking about how they continue to take phentermine despite no longer needing to lose weight or becoming dependent on it. They begin to take more and more each day to get the same effects.

Phentermine has a limited period of efficacy due to its amphetamine-like structure and addicting effects, so taking it long-term gives you fewer and fewer of the desired effects of appetite suppression and additional energy and more chance of dependence and suffering from dangerous side effects.

Other threads indicate that users doubt the addicting effects of phentermine or consider that it wouldn’t happen to them, and while individual differences mean that not everyone would experience severe side effects or dependence on phentermine, it is undeniable that phentermine is an addictive medication, shown by the withdrawal symptoms that many experiences once they stop taking phentermine.

For this reason, it is important always to follow your doctor’s instructions, so if you find that your phentermine prescription does not produce the same effects, you should not increase your dosage to manage your tolerance.

Doing this will only lead to a greater dependency and, therefore, a greater chance of withdrawal symptoms once your prescription ends.

This adaptation and tolerance to phentermine is the core reason for withdrawal symptoms, as strong medication can be highly reactive and addictive to the body.

Furthermore, it is important to remember that as phentermine is similar in structure to amphetamine, we cannot be sure that long-term usage doesn’t harm the body in some of the ways that amphetamine does when taken long-term.

Since no medical trials have extensively tested the effects of taking phentermine long-term, we would have to base our knowledge on the long-term usage of other amphetamine-like substances, which would therefore indicate that heart damage might occur, in addition to psychological damage or other unpredictable reactions.

Long-Term Weight Loss Without Taking Phentermine Long Term

Phentermine is not a miracle pill, but rather a tool kick to start your weight loss journey and should be used only as a means to establish a routine of healthy eating habits and exercise to continue for life.

If phentermine is taken without any effort to change the lifestyle in other ways, then it is to be expected that weight gain will occur once the phentermine prescription finishes.

But weight gain following the cessation of phentermine is no reason to take phentermine long-term, as this will just delay the inevitable, in addition to putting your health at risk.

To avoid the possibility of dependence while still taking phentermine, you should build yourself up to face the end of your prescription by using phentermine as a tool to help you achieve a maintainable healthy lifestyle.

As part of the best phentermine weight loss schedule, as well as eating healthily and exercising, it is important to establish a good sleeping routine and to take time to de-stress and look after your own well-being and emotional needs to create a balanced routine whereby you can continue to lose weight or maintain your goal weight without phentermine.

A great way to continue this balanced routine is to use a weight loss supplement such as Phen Caps to manage the end of your phentermine prescription.

Like phentermine, Phen Caps suppress appetite, reduce cravings, and increase energy, but they have no side effects and can be taken for as long as you need to achieve long-term weight loss.

Have you been taking phentermine long-term? If so, we’d love to hear from you if you have any feedback or questions, so please comment below!

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  1. I have been taking it for about 7 years now. I have many concerns I most recently went on a 2 month midlife crisis or something I gambled every penny I had then money I didn’t have I can’t control myself. I’ve made horrible decisions. My impulse is completely gone. I am seeking help, but just wanted to put this out there for long-term users for knowledge also, I have had other problems with my eyes and my hart rate.

  2. I would like to know how the users that now have serious issues such as heart problems have it diagnosed. Did you go to a doctor stating certain symptoms to get certain tests performed?

    I have used phentermine for 10yrs on and off (more on than off) and always have doubts if I am developing heart issues.

  3. I have been taking phentermine for 21 months. I started out at 302lbs and I am now 217lbs. I have been relatively healthy. Only having hypertension and hyperthyroidism fir most of my life. My cholesterol has always been perfect. 4 weeks ago I suffered from 5 ischemic strokes on both sides of my brain. This came out of nowhere. Am I safe in assuming the long term use of phentermine was the cause?

  4. I have been taking Phentermine almost 2 years I now recently stopped losing weight it isn’t working like it did in the beginning l, however I have lost a little over 100 pounds. I haven’t made my weight loss goal yet how long should I stay off them to get the same effect as I had from the beginning? When I stop them do you think I should cut back a little at a time or just stop completely?

    1. Hi Clarissa! It’s typically best to wean off phentermine, especially if you’ve been taking it long-term. However, your prescribing physician is the best person to talk to about strategies to avoid phentermine withdrawal, as well as options for continued weight loss after phentermine. Make sure to talk with him or her before any making any changes to your daily dosage/routine.

  5. Hello,
    I had taken Phentermine years ago for a couple years. I haven’t taken it in years, like 4 now, but I was recently diagnosed with CHF and the valves in my heart are abnormal, not saying the med caused this, but I was healthy, no family history of heart disease, had yearly physicals with no indications of any heart abnormalities. Just wanted to say, it’s a powerful drug and it does help with appetite suppression, hence aiding in weight loss, but be careful.

  6. I was on this medicine phentermine 37.5 for 5 1/2 years straight. Never came off of it took it every day and I can honestly say that i never abused this medicine not one time. I took it like I was surposed too. I’m off of it now but it done alot of damage to my body over the 5 1/2 years I took it. I will never ever take this medicine again. I just hope anyone who is on this medicine I pray you get off of it. It’s very bad for you. There’s other ways to loose weight.

    1. What did it do to your body? Is the damage reversible? I’ve been on and off adipex for 20 yrs no real problems I did have to get glasses for distance but not sure if that had anything to do with it being I’m in my 40’s and my whole family wears them. I was thinking about trying them again to help with weight gain but Lil nervous now that I’m getting older.

  7. I’m a 30yo female and I’ve been taking Phentermine on and off for almost 10yrs now. The only side effects I’ve noticed are dry mouth and dry eyes. I’ve noticed it doesn’t necessarily help me lose weight anymore but it does control my appetite and wakes me up better than coffee. When I stop taking it I might as well have narcolepsy. I take it mainly to maintain my weight and wake up to function. I haven’t noticed any problems when stopping the medication other than tiredness and wanting to inhale any food in sight. I am concerned about long term effects of the medication because hypertension and heart disease runs in my family. I will admit a dependence to it because it’s convenient and the energy it gives me. Any recommendations to break the dependence for good?

    1. Hi Carolina, thanks for your comment! We would suggest speaking to your doctor. He or she can work with you to reduce usage and ultimately get off phentermine. The fact that it no longer helps you lose weight is another indication that your body has developed a tolerance to the medication. Still, you’re wise to be concerned about the long-term effects of staying on phentermine and you’re awareness of the dependence means that you’re already moving in the right direction. So, we would suggest a doctor’s visit as the next productive step. Best of luck!

  8. I started about 9 months ago and it worked so well. I have sleep apnea and was about 100 pounds over weight. I have major food cravings and drink alcohol on weekends that contributes to my weight. I had so much more energy taking Adipex and was almost never hungry. I ate eggs in the morning, veggies for lunch, and a piece of meat for dinner. I exercised a few times a week, but suddenly had energy to run on the treadmill. I lost 40 pounds over four months. My doctor said I had to switch off of it so I went on Contrave. I maintained the same diet, but had less energy to exercise. I gained back 10 pounds during the 3 months of Contrave. My cravings were slightly less than normal on Contrave, but I felt like I had no metabolism or energy. Started my second round of Adipex this month.

  9. Hello
    I’m 32. Have been on adipex about 5 weeks. Ive taken it before, a few yrs ago, but got pregnant (long after I stopped taking the med) and have had trouble getting back into shape. I don’t take it every day because I work night shifts 3 days a week, but stay up during the day when I don’t work. I started taking it now to help with energy to work out. I have energy troubles due to my work schedule. I’ve not experienced any of the side effects I did last time, insomnia, palpitations, etc. I have a slight reduction in my appetite, but nothing like last time I took it, thankfully. The first time the idea of any food was appalling. However now I’m not getting much energy boost, after only 5 weeks. Just wondering, since I’m not experiencing any side effects, no increased heart rate or BP, no palpitations, or high blood pressure, nothing but maybe slight indigestion sporadically, what risks would I be taking if I took it every 12 hrs once or twice a week? I wouldn’t run out bc as I said, I don’t take it every day. For instance, if I took my meds at 5pm yesterday, would taking one or a half tab at 8 am the following day pose any risks to my health? My prescription is the 37.5mg

    1. Hi!

      For ANY change in dosage, or adding any additional medicines, drugs or supplements of any type while taking phentermine, we STRONGLY suggest talking to your prescribing doctor. Although it is good that you’re not having any of the nasty side-effects of the first time, you’re still taking a very powerful drug at the highest legal dosage. Consult with your doctor first to see what are your options.



  10. I began a successful phentermine journey in 2011. Phen was prescribed by my family med doc for a duration of 7 months. During this time I lost 50 lb’s. It was a great experience and I kept the weight off for close to 4 years. I started having issues due to pre-menopause and my doc started me on zoloft and then prozac.
    though I continued to monitor my eating habits, and exercised 3x per week, the weight kept coming on. My doc checked full blood panel. Her only suggestion to the weight gain was the use of the anti-depressants.
    In early Feb of 2016 the same doctor put me back on the phen. i busted my ass to lose the weight, but it was coming off VERY slowly. I feel much better, Im even more active, my blood pressure has gone down, and I have lost 26 lb’s.
    Unfortunately, change in insurance caused my providers to be changed. I was with Sutter but now a clinic based provider. My doctor of 20 years wrote up a full description of me. it directed my new doctor to continue the phen throughout December of 2017, discuss the possibility of change in anti-depressants, and taper down phen throughout a months time till I depend on myself for eating and workout habits to continue. My doctor also documented that the new provider continue to monitor my weight as she had done.
    Yesterday I saw my new provider for the first time. He was very rude! He ordered me off of the phen immediately without tapering me and lectured me about the risks of the medicine. He then said he was ordering an echo cardio gram. He also took me off of my current anti-depressant of prozac, because again, “he didnt approve”.
    Im nervous about the expertise and opinion of this new physician. Also about gaining the weight back and not feeling as good. I worked hard, and was looking forward to reaching my goal, and continue monitoring my health & weight.
    Any sugesstions?

    1. Hi Teena!

      Doctors have the final word regarding advice on phentermine use and other medications. That being said, if you do not feel comfortable with any doctor, you can look for a second opinion too. Best of luck!



  11. Ok so my dr prescribed me phentermine 3 months ago and I have lost about 40 pounds but I’m not to my target weight. I was 180 pounds at 5’3” and now I’m 141, I was hoping to get to 125. Anyway Rx is about out and dr told me I’m on my own. Problem is it has helped my depression, RA and Fibro SO much like no other med and I’m afraid not only to gain the weight back but to get depressed and have pain again. What do I do now??? It may be addicting but he won’t prescribe it so what do I do now?

    1. Hi Tracey! We would suggest speaking with your prescribing and/or primary care doctor about the other benefits you’ve seen while taking phentermine, and asking if there is an alternative medication that he or she could recommend. While it’s not advisable to take phentermine long-term, there may be other options that could help manage your depression and pain similarly. Best of luck!

  12. I’ve been on phentermine consistently since 2011 only stopping for the 9 months I was pregnant. Only side effects I’ve noticed is the dry mouth as sell as more difficulty falling asleep. It still curbs my appetite and gives me the boost of energy. It puts me in a better mood and makes me feel like I wanna get things done. Lately I’ve been noticing I feel short of breath and can’t hold my breath for as long as I could before. Wondering if that has anything to do with the phentermine and if anyone has experienced the same problem. Any feedback will helpful and greatly appreciated!!!

    1. Hi Shari! Shortness of breath can indicate a serious phentermine side effect, so we would recommend speaking with your prescribing doctor about this ASAP. It may also be caused by something else, but your doctor would be best able to determine why you’re having trouble holding your breath and help you solve it.

  13. I started taking phentermine in 2008 before I had my first son. I lost weight quickly and felt great. There was a sudden ” speed” like effect I experienced for the first couple of weeks but that wore off. I took it for about 6 months. Then I became pregnant. Few months after giving birth I got back on it. Worked just like the first time. Lost weight quickly. I was on it the 2nd time for about 1 year , maybe 1 year and a half. Then I became pregnant with my 2nd child in 2011. About 5 months after giving birth I got back on it to lose the baby weight. This 3rd time I was on it for about 6 months this to a year give or take. Had no problem losing the weight and kept it off until I became VERY sick in 2015 while taking it. Long story short I found out I had Myasthenia Gravis disease. Affects all your voluntary muscles. First one in my family to have anything like this. It interferes with transmission of signals from your brain to your muscles. I quit taking while I was sick. Skip forward to present day. I got a month supply since I have gained weight from the steroids I had to take while sick and actually being able to eat. Mind you I have been in remission of MG the last 2 years. Well upon taking phentermine currently I’ve noticed my MG symptoms come back. A doctor has not confirmed with but in the back of my mind I feel phentermine has caused the Myasthenia Gravis. Please beware of long term effects. You don’t want to end up with a life long incurable illness for a quick fix of weight loss. Completely not worth it. I almost lost my life when I was sick.

  14. I have been on Phentermine 37.5mg capsule since 2003. I have taken a few breaks over the years but not more than 6 months before needing to go back on it. My story a little different from most here. I have been a fitness pro for over 25 yrs. From 1999 – 2002 I’d began to gain weight and experience extreme lethargy to the point I’d get nauseous. Long story short, went to many dr’s when an endocrinologist sent me to have a true metabolic study done. By this time I’d gone from 120lbs to 150lbs and that was with 2 work outs a day, plus training clients and eating down to 1200 Cal a day.

    Study came back I was only burning 890 Cal a day even w/ my muscle mass. I also had low heart rate, BP & body temp. Dr said my central Nervous system was almost dormant and started me on phentermine. It worked as weight started coming off, I could stay awake and not get nauseous from fatigue and my mood improved (well I was extremely depressed being a trainer w/ a weight problem)

    I got breast cancer in 2008 and was off them for about 9 months. Then all the symptoms crept back. Went off again in 2013 for about 6 months and symptoms came back.

    While taking them my HR stays mid 60’s, BP hangs around 100/70 and body temp 97.9- 98.1. I have had a few echo cardiograms over the years w/ my latest one two weeks ago, all normal. Biggest side effect is dry mouth and blood pressure drops when I stand up too fast (but that happened before)

    However, I was recently diagnosed w/ lupus and am undergoing additional tests as it seems to have attacked my lungs & kidneys. I have a team of three dr’s: internist, endocrinologist & rheumatologist. Internist says adverse affects of phentermine. Endo & rheumatologist says not related at all. But I’ve just started this new journey so I suppose I must consider all possibilities.

  15. I have long term experience with Phenterminel on and off for over 20 years. I admit dependence, however I have stopped when they were no longer effective. My doctor monitors me closely, and if I were not able to get them, I fear what alternative I might take, since I was an amphetamine user in my teens. I am now age 50, my blood pressure is outstanding, and have no major health issues. In fact I worry what would happen if I stopped.

  16. I am a type 1 diabetic, I developed it when I was 8. Im now 45 and Ive been on phentermine off and on for probably 5 years. Dry mouth and speed are the two side effects that are worst for me. I go off the medicine for a few weeks when my 30 day prescription runs out because I have gotten so used to it, it stops working with my weight loss efforts. The lazy feeling that comes with stopping is almost unbearable. I wonder about the long term with my heart and I see where some people have developed vision problems. Is vision loss a side effect of phentermine? BTW, Istarted phen to lose weight. Im still 200 +, it only allows me to maintain my weight. I keep hoping stopping/starting will help me, it never has. I hike at least 20 miles a week, I eat right and exercise. I dont know if the side effects are worth the energy boost and hopefullness of losing weight. Wish it worked for me better. Not real sure what to do.

  17. I am a 50 yo female and have taken phentermine on and off for 20 years now with no side affects whatsoever. I do notice that the effects of it have greatly reduced but they still continue to suppress my appetite. This medication is not intended to be stopped abruptly as it will have adverse affects. It is best if you wean off the medication.

  18. I’ve taken Phentermine recently (4 weeks), my weight loss is not significant, however it has reduced my cravings. The most unusual result however is that I sleep better? I take half a pill around 10am, around 2:30 I take a 30 min restful nap. Then easily go to bed around 9pm, aking at 5:30am. Years ago I took Nuvigil prescribed by my sleep doctor. I do not have apnea, I was diagnosed with excessive sleepiness. Nuvigil is no longer available for my condition, she recommended Ritalin, but I passed. I received the Phentermine from a weight loss clinic. This is given me better rest, and better wake cycles, I sleep more restful. Is this been noted before for helping sleep issue patients? I understand some struggle going to sleep, but this helps me sleep better and more restful.

  19. I have been on this medicine for two years. It has helped me loose weight and I feel so much better about myself. The only side effect that I have is the dry mouth. I use to have to take medicine for acid reflex but since on the Phentermine I no longer take the omeprazol. My blood pressure is perfect and I do not take blood pressure medicine. This has been a miracle for me.

  20. Hi I have been using this medication for nearly 4 years. At the beginning I used 37.5 dosis to lose the 40 lbs I wanted but then I have been taking only half of this to keep me fit; it helps me not to eat too much as I do without it. Thanks to God that I found this website because the problem is that now I have been feeling pain in my chest, shortness of breath, tachycardia. I was always very healthy so I wonder if these symptoms are because the phentermine. I will make an appt for my doctor ASAP.

    1. Hi Yullet,
      From what you say it’s highly likely that the side effects you’re experiencing are a result of phentermine. We would advise you to stop taking phentermine now rather than waiting to speak to your doctor.