phentermine dosage

Although phentermine 37.5mg is the most popular and well-known phentermine dosage, there are a wide range of dosages to choose from when it comes to being prescribed phentermine. So, if you’re not sure which is the best phentermine dosage for you, or you’re wondering why your doctor has prescribed you a certain dosage, then we have all the answers for you!

The Phentermine Dosage Options

Although international phentermine brands such as Duromine are available in higher dosages, the phentermine dosages available in the US range from 15mg to 37.5mg. The mg or milligram amount refers to the amount of phentermine hydrochloride (phentermine HCL) in each capsule or tablet. Phentermine HCL is the active ingredient of phentermine and phentermine brands such as Adipex. Phentermine capsules and tablets contain other ingredients but these are inactive ‘filler’ ingredients which are not taken into account when referring to the phentermine dosage.

Generic phentermine, which refers to phentermine made by a variety of pharmaceutical companies under the name ‘phentermine’, as opposed to any brand name, comes in 15mg, 30mg, and 37.5mg dosages. While phentermine capsules are available in dosages of 15mg, 30mg and 37.5mg, phentermine tablets are only available in the highest dosage of 37.5mg. However, some doctors choose to prescribe the 37.5mg phentermine tablets to be split in half, to be taken either as two doses of 18.75mg during the day, or as half a tablet per day.

The most well-known phentermine brand, Adipex, comes in both capsule and tablet form, but is only available in the maximum dosage of 37.5mg. By comparison, the phentermine brand Ionamin is only available in capsule form in dosages of 15mg and 30mg. Phentermine is also available as an orally disintegrating tablet (ODT) under the brand name Suprenza, ideal for those who have difficulty swallowing capsules and regular tablets, known as dysphagia. Suprenza is available in 15mg and 30 mg dosages, however due to the way the tablet starts to dissolve immediately, these dosages are equivalent to a base phentermine dosage of 12mg and 24mg respectively.

What Determines Your Phentermine Dosage?

If your doctor decides that phentermine is right for you, he or she will then determine your dosage based on the amount of weight you have to lose, your age, lifestyle, and whether you have any additional medical conditions, among other factors.

In general, doctors will prescribe the lowest dosage of a medication needed to provide the desired effects. However, in the case of phentermine it is quite typical for patients taking phentermine to start off with the maximum dosage of 37.5mg for two reasons. Firstly, phentermine tablets are more commonly prescribed than capsules, and secondly, the most popular phentermine brand, Adipex, is only available in this maximum dosage. In addition, as phentermine is intended for the short-term management of obesity, and is typically prescribed for 12 weeks at a time, both doctors and patients often find that taking the highest dosage is the best way to maximize the patient’s limited time on the medication. So, if you’re new to phentermine and you’ve been prescribed the maximum 37.5mg dosage, this is actually quite common.

Some doctors prescribing phentermine tablets may advise you to start your phentermine prescription by taking half a pill, equivalent to 18.75mg, for the first few days. This allows your body to get used to the effects of appetite suppression and added energy more gradually, and means that the side effects such as dry mouth and insomnia should be less severe than if you were taking the full 37.5mg dosage. Alternatively, your doctor may tell you to split the dosage and take 18.75mg before breakfast and again before lunch to spread the effects out throughout the day, which is particularly useful if you usually experience cravings later in the day.

phentermine dosage

If your doctor chooses to prescribe you phentermine in capsule form, then he or she will have more choice when it comes to deciding which dosage is more suitable for you. Phentermine users taking capsules can start on either 15mg, 30mg, or 37.5mg, or there is also the option to take two 15mg capsules per day, splitting your dosage by taking one before breakfast and one before lunch. If it is thought that you may be sensitive to the effects of phentermine, or if you have previously experienced sensitivity to medications, then are likely to be prescribed the lowest phentermine dosage of 15mg to start with. Additionally, if you have other conditions or medications to take into account, a lower dosage might be preferable to avoid the possibility of an interaction. If you are prescribed the 15mg phentermine dosage to begin with, your doctor may intend for you to work up to 30mg capsule after a certain period of time, or you may be advised to take one 15mg capsule in the morning and a second 15mg capsule before lunch. But, if 15mg is sufficient for you to consistently achieve the desired effects then it would not be necessary to increase the dosage.

Does A Higher Phentermine Dosage Mean Faster Weight Loss?

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. By comparison, although lower dosages of phentermine tend to give patients fewer side effects, they may not always give patients the desired effects of appetite suppression and added energy to a sufficient enough level for them to really change their habits and successfully lose weight. Therefore, it’s a case of getting the right phentermine dosage for the individual, which can often be a balancing act between minimizing side effects and maximizing weight loss. The right phentermine dosage for you is one that helps you to control your appetite, boosts your energy and motivation, but that doesn’t cause you any unmanageable side effects.

If a lower dosage of phentermine is working for you to suppress appetite and add energy and is also helping you to lose weight then this is a good thing, as it means your body is not building up as much of a resistance to the phentermine as it would if you were to take the maximum dosage. It’s also likely that any side effects you’re experiencing are mild and manageable. By comparison, those who start off on the 37.5mg dosage often find that they suffer with much more severe side effects, which can in turn stall their weight loss progress. For example, side effects such as insomnia can negatively affect weight loss as sleep is crucial to ensure that your body is burning fat and keeping a steady metabolism. It’s also not uncommon for people to stop taking phentermine altogether due to the extremity of side effects for some patients. If you feel that your dosage might be too strong for you, we would advise you to speak to your doctor about taking a lower dosage for the first week or two to allow your body to get used to the effects.  Similarly, if you feel that your dosage is too low and that phentermine is not helping control your appetite and boost energy then you should not increase your dosage without first being specifically instructed to do so by your doctor.

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What phentermine dosage have you been prescribed? Let us know your experiences by commenting below!

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48 Responses

  1. I’m begining my phentermine journey. This article will help me greatly

  2. Thanks so much for this article! I just started Phentermine today, and was quite surprised and rather concerned when I saw that I’d been prescribed the maximum dose straight out of the gate. This article has helped me to understand why my doctor did this. It also has helped me understand questions I can or should ask my doctor if side effects are too severe.

    • Hi Alicia,
      Thanks so much for this feedback, it’s great to know that you found the article helpful! Good luck on your phentermine weight loss journey!
      Sally, phentermine.com

  3. keep sharing your information regularly for my future reference. This content creates a new hope and inspiration with in me

  4. I have been taking 3 X 37.5 pills a day since April. Started at 277 lbs. I am now at 215. I am a 34 year old male.

    • You are taking 3 37.5mg a day? I seem to have to take 2 a day is that bad?

      • Hello Cassie. 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. https://www.facebook.com/groups/1069871763087734/

        Rebeca, Phentermine.com

  5. I started out on the lowest mg & lost 10 pounds within 2 weeks. I had to quit taking them due to being expensive. I went back on sometime later & was put on the highest mg & took a half one every day & then upped it to a whole one everyday & I didn’t lose. The lower mg does a lot better for me.

  6. I simply cannot find a Diet Dr in Or near Lakeland, Fl. Anybody know of a Dr in or near me?.. Thank you.. Douglas..

    • Hi Douglas,
      You might have more like getting a response on our forum. Here is the link for you to register if you’re not already on it: https://www.phentermine.com/forum/register.php
      Sally, phentermine.com

    • I go to doctor gahlay for weightloss

    • There\’s a doctor in Avon park Florida that prescribes adipex. He does internal medicine. It\’s $50 for the appointment. I\’ve been going to him for years and my sister as well. 1005 west circle street Avon park Florida 33825

  7. I lost 60 pounds on phentermine and toparamite. But the insomnia was too much. I would get 3-4 hours a night of sleep, than the pills stopped working and I have gained it all back in 5 month. Heart broken. Will try again. But at a lesser dose.

  8. As a RN I’m baffled as to why everyone is talking about how much to take vs how much not to take. Let’s talk about two other highly mitigating factors to weight loss. Healthy eating and at least 30 min of exercising. You can take a ridiculous amount of 37.5 3 x a day like that guy above, but you’d better pray you don’t suffer from s high BP, pulse or arrhythmia problems. The key to keeping a healthy weight should be managed simply by eating healthy and AT LEAST 30 min of exercise a day. If you do not implement that practice into your lifestyle you can take all the phentermine you want and you still be unhappy w your results. Having a nice body does not come from a pill/tablet in a bottle.

    • Adrienne, I am an RN as well however for some people it isn’t that simple. If they are monitored by a Dr, 99% of the time exercise and nutrition is part of the plan. I took Phentermine years ago and it helped me get on the right track. Clean eating and exercise alone didn’t help me because I gained weight from stressing and hormone issues. As a medical professional, we should always be empathetic. The same way doesn’t always work for everyone. And not everyone has weight issues because they are overeating. Many times people don’t eat enough (Once a day) and it causes the body to store fat.

      • I am not a health professional but I agree with Key; it\’s not always that simple. I live with several chronic health conditions, including asthma, fibromyalgia, and hypothyroidism. Just in the last six weeks I had breathing issues which landed me on Prednisone for a total of 4 weeks, and anyone who has taken a steroid knows that, along with it, can come weight gain. For me, it always does. I need help losing weight so my doctor prescribed Phentermine and I\’ve started with half a dose. I\’m only on day two but it is already helping me control my crazy cravings and my goal is to relearn how to eat in a healthy, more balanced way. I think the main goal for most is to use this medicine as a tool, not a crutch. At least I would hope so. It\’s definitely my goal!

  9. I Have taken one 37.5 a day or over 3 years to improve my energy. I wake with very low blood pressure& pulse. This helps me to get up and get through the day. I recently met another lady taking 2 a day. I asked my doctor to up my prescribed dose and she is leary to do so. Is it uncommon to take 2 37.5 a day?

    • Hello Evelyn. 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. https://www.facebook.com/groups/1069871763087734/

      Rebeca, Phentermine.com

  10. I started Phentermine 15 mg today. I have been watching what I eat but I am starving. It is not suppressing my appetite at all.

    • Hello Marsha. Thank you for reaching out.
      Phentermine is known as an effective weight loss medication, helping users to lose weight by suppressing appetite. However, that doesn’t mean that you won’t still get hungry on phentermine. Here we explain why you might still be feeling hungry and how to manage your appetite to help boost your weight loss results: https://www.phentermine.com/blog/hungry-phentermine/

      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. https://www.facebook.com/groups/1069871763087734/

      Rebeca, Phentermine.com

    • I started a couple of months ago 1 pill a day. I have lost 8 lbs. I\’ve been eating right and exercising and can\’t seem to lose anymore. I\’m hungry all the time and it seems like it\’s getting worse. I do eat healthy meals and snacks. I tried cutting out the bread bc that was my weakness but I would end up with a migraine. Seeing everyone else\’s good results, it\’s very frustrating

  11. If you were to take 2 37.5mg a day when is the best time to take them? Before breakfast and lunch?

    • Hi Mel,
      Yes, usually when patients are taking two halves separately they find that taking half first thing and then the other half around 30-60 minutes before lunch is the best way to take phentermine like this.
      Sally, phentermine.com

  12. I started Dec 6 2016, I have been out of them since middle of April until yesterday, I was on 37.5 tablet during that time, however I have only lost 20 pounds, with eating low carb drinking nothing but 112 oz of water, when I went back yesterday she gave me a script for the 37.5 tablet and 30mg capsule and instructed me to take them both at 6am in a little timid to try this , yesterday I took the tablet today I took the capsule but I am curious if that is too high of a dose I don’t have many side effects other than dry mouth, i started at 221 in December I’m 200 today she prescribed it to me because I will go 2 weeks at a time losing and gaining the same 2-4 pounds then finally a drop and then the 2 week bouncing again and it has gotten frustrating, just curious for any opinions?

  13. I have been on phentermine and topirimate for 2yrs went from a 22 plus size to a juniors size 13 im 36 never felt better and my bp has never been over 110/54

    • What dosages?i was prescribed both 37.5 of phentermind and 100 of the topirimate.I lost 18 lbs n 3 wks but the topirimste made me feel terrible.Like I was high n sence.Very irritable,ect..

  14. I am confused. My doctor just started me on phentermine tablets / Adipex. The tablets come in 8mg doses and she has me starting at that dosage. I understand why she wants me to increase gradually and I have, not surprisingly, not felt a thing at 8mg. According to my doctor, the maximum dosage for these pills is 24mg but everyone keeps talking about a 37.5 tablet / capsule. Is she wrong about the dosage or am I confused? Please advise.

    • Hi Jennifer! You are correct that there is a 37.5mg tablet/capsule of phentermine. However, it is not uncommon for doctors to start patients on a lower dosage and increase slowly, and your doctor may have a reason for feeling 24mg is your maximum dosage. We would suggest speaking with her if you are concerned about the dosage she has prescribed. Do not take more than your prescribed amount without speaking to your doctor.
      Best regards,
      Rachel, phentermine.com

      • Thank you for your reply. I double checked and my tablets are called Lomaira (phentermine hydrochloride). I just want to double check because I think my doctor thought that the maximum dosage for this was 24 (not just for me but for this medication). We are being careful and starting slowly (hence the low dosage) but I also want to be successful. I am now taking 16mg and not feeling any effects. I am absolutely following her advice and instructions but I just want to be clear on the dosage range for this particular medication. This is her first experience with this medication and I just want to make sure that she is correct about the dosage range. I am confused about all the different names and forms that this medication comes in.
        Please confirm the dosage range. Thank you.

        • Hi Jennifer, I’m glad to hear you are working so closely with your doctor! The currently available range is 8mg to 37.5 mg. You may be interested in this page about dosage, just keep in mind that is has not yet been updated to include Lomaira (the 8mg tablets you are taking) given the relative newness of the medication.
          Rachel, phentermine.com

        • My first time on Phentermine, too, but since no one is quite answering your question accurately, figured I\’d take a stab at it.

          Phentermine (hydrochloride) is the active ingredient. It is prescribed in two popular brands.
          Adipex, which is available in 15mg-37.5 mg
          And Lomaira available only in 8mg.

          The purpose of Lomaira at such a lower dosage is to be able to prescribe it 3 times a day before meals, equalling 24 mg a day. Versus Adipex at a higher dosage once a day, but occasionally prescribed as splitting pill in half twice a day.

          Basically you should take your 8mg Lormaira a half hour before each 3 meals a day to sustain a constant lower effect all day. Some times that late evening one causes insomnia and people fair better on the one morning dose of Adipex (also causing a stronger effect). It depends on the individual and the goal is to find the lowest dose on either that accomplishes the desired results.

          I am not a doctor and my findings are my own personal opinions. I would recommend talking to your doctor about trying your Lomaira 3 x a day at 8mg and if it does not reach your desired effect after a couple weeks, consider switching to Adipex.

          Hope this helped

          • Thanks so much for your comment, Amanda! Lots of great details and very helpful 🙂
            Rachel, phentermine.com

  15. Ok, so I\’ve got a bit of a complicated medical history. The long and short of it is that my thyroid was removed about 8 years ago. Since then, my thyroid levels can\’t seem to get regulated, no matter what thyroid med I\’m on. I\’ve been on Synthroid, then Armour, now I\’m back on Unithroid. On top of the thyroid issues, I suffer from Fibromyalgia and Thalessemia.

    My doc recently prescribed me the 37.5mg dose of Phentermine to help me in my weight loss journey. My weight spiraled out of control, and quite quickly. Come to find out my TSH (thyroid stimulating hormone) was way out of range- at a 43. So I\’ve been taking the Phentermine without success. In fact, I\’ve still been gaining. Should I bother taking the Phentermine while my thyroid is so out of whack? I\’m totally lost.

    • Hi Carly, thanks for your comment! Given your complicated medical history and the fact that you’re already working on this with a doctor, we’d recommend speaking with your prescribing doctor (or primary care physician) about your concerns. He or she would be best able to asses the appropriateness of phentermine in your particular case. In the meantime, you may be interested in our article about phentermine and thyroid.
      Rachel, phentermine.com

  16. I have taken phentermine and topamirate for 3,4 months now ,have lost about 18-20pounds .also after stopping my Lyrica. No good for me. I had gastric bypass in 2013 was 297 at one time then had surgery at 270. Lost down to 180, got an injury and gained some back now I\’m working on re-losing it after gaining. Lyrica had my gain 45 lbs in 2 months no joke! Im floating around 235…sigh. .Because soon as I quit, I started dropping. Anyway…I take 37.5 mg a day ..but I really metabolize med SUPERfast! Meds don\’t stay in my body., like alcohol…I\’m a cheap date.
    Pain relievers…etc. I am not feeling this in my system any longer. Maybe I should go to a lower dose and split it up to sustain it. Like 18mg 2X aday or even 24 2X a day …I really have a high tolerance. Why also I can\’t take legal opiate pain relievers.None at all. I stay away. Phentermine.com?

    • Hi Carol, thanks for your comment! We recommend speaking with your prescribing doctor if you feel your dose/schedule are no longer effective. He or she would be best able to adjust your prescription in conjunction with your other medications and conditions. You should never adjust your phentermine dose or schedule on your own without speaking to a doctor first.
      Rachel, phentermine.com

  17. your article is more useful and informative.. thanks to share this… keep rocking..

  18. I used to be on 37.5 but they cause me to be depressed so my Dr put on the 30 Mg. Now he has retired and I can\’t find a Dr who will prescribed them to me. My Dr.doesn\’t believe in that. So I need help. I\’m 35 pound over wieght since my divorce.

  19. About a month ago I started Phentermine Hydrochloride 37.5mg to manage my cravings and eating habits. It has helped with the cravings, eating habits and I\’ve lost weight, however, what is has helped with the very most is my ADD, which I do not take meds for. I\’m 48 yrs old and my psychiatrist feels a stimulant would create heart issues. I have great blood pressure, it\’s not been an issue for me. It has literally changed my life, my relationships, my work performance…it\’s touched every aspect of my world. Have you come across this before in relation to ADD/ADHD and if so, do you find that taking a higher does of 37.5 would be beneficial for that condition?

    • Hi Angela, thanks for your comment! Your reaction is not unheard of given that phentermine is a stimulant, similar to other ADD meds. Still, it is NOT advisable to exceed the maximum daily dose of 37.5mg of phentermine. This maximum dose is related to both the medication’s addictive potential, and an increased risk for serious side effects. We are not qualified to offer medical advice, so we would recommend speaking with your prescribing physician and psychiatrist if you are interested in further management of your ADD. Do not adjust your phentermine dose or schedule without speaking to a medical professional first. In the meantime, check out the forum to read about other users’ accounts of similar experiences (there’s a search bar at the bottom)!
      Rachel, phentermine.com

  20. I have taken phentermine off and on for years and it really helps me. I start getting used to it after a while. How long should I take. Break from it to really get it out of my system so that I can get the full effects once again? Thanks.

    Krista

    • Hi Krista, thanks for your comment! It varies a lot person-to-person, but the general recommendation is at least one month (or whatever your doctor deems appropriate) between rounds. Still, many repeat or long-term users report that phentermine is never as effective as it was the first time due to the body’s retained tolerance. Even so, you should NEVER take more phentermine than prescribed – either by taking more medication or by taking it more often – due to the increased risk of serious side effects.
      Rachel, phentermine.com

  21. I weigh 455 pounds and take 1-37.5 MG daily…..I have been gaining a few pounds every month. Because of back problems I can not exercise…..I can only walk about 30 yards before my back gives out. I am an old Meth head, so I think that us why I gained so much wieght to begin with…..my body storing it all……and never got out of that mode. I was thinkingmaybe two pills a day……but afraid my doctor would say it\’s too much……it worked for about the first month I was using it…..but now not so much. I was thinking twice a day would get me over that afternoon hump…..idk……what do you all think?

    • Hi Del, thanks for your comment. We recommend speaking with your prescribing doctor about your increased tolerance to phentermine, as well as your medical history (if he or she is not already aware). It is not generally advisable to exceed the maximum dose of 37.5mg per day due to an increased risk of serious side effects. However, we are not medical professionals so we strongly suggest speaking with a medical doctor about your specific concerns. That being said, it is normal to develop tolerance to phentermine. Instead of increasing dosage, this change is usually a reason to consider coming off the medication. NEVER adjust your dose or schedule without speaking to your doctor first, and ALWAYS take phentermine exactly as prescribed.
      Rachel, phentermine.com

  22. Hi,
    I started taking 15mg of Phentermine capsules but I am hungry literally like every 2 1/2 – 3 hours. Sometimes my stomach hurts from how hungry I feel. I don\’t think that\’s normal. Any suggestion?

    • Hi Mina, thanks for your comment! New users are not usually as hungry as you describe, so we would recommend speaking with your prescribing doctor about adjusting your dose and/or schedule (reminder: NEVER adjust it on your own). Also double-check that you are eating enough to keep your body fueled and staying hydrated. Best wishes!
      Rachel, phentermine.com

  23. Hi there, I\’m on my second day of Phentermine and it has been a struggle. I\’ve been experiencing some of the side effects, but my bigger concern is my mood. I get that boost of energy and then halfway through the day my mood is very low. I hate that feeling. I know it\’s only day 2, but I\’m wondering if it might help to cut my pill in half like suggested? The only thing is I\’m only taking 15mg. Can I take half in the am and half at lunch? Will these side effects go away? I just want to feel like my normal self while taking the pill or else maybe it isn\’t for me. I believe my doc has me on the lower dosage on purpose. I only have 20 lbs total to lose. I\’m 32, 150 lbs currently. Any feedback or advice would be great! Thank you!

    • Hi Robyn, thanks for your comment! It’s actually relatively common to experience this low mood while on phentermine. You may be interested in our post on depression on phentermine for some explanation plus ideas about how to deal with the lows. If you’re still interested in adjusting your phentermine schedule, we suggest speaking with your doctor first. Not all pills can be split in half, and you should never adjust your dose or schedule without speaking to your prescribing doctor first. He or she may also have some other good suggestions about coping with the lows another way. Best wishes!
      Rachel, phentermine.com

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