phentermine dosage

Your Phentermine Dosage Guide

General Phentermine Questions?
Check out the ultimate guide to phentermine weight loss pills!

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.


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

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76 Responses

  1. 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… 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.

  2. 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!

  3. 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!

  4. Hi. I took Adipex for a month, went off it for a month, and now am back on it. Both times, I\’ve gotten painful mouth ulcerations, gotten these weird facial tics, and experienced insomnia despite taking Trazadone. I\’ve also not had experienced the fabled \”energy\” rush, but that may be due to the insomnia. I\’m going to try cutting back the dosage for a week and see how that works, but I did want to let you know about the side effects for your clinical studies. Thanks.

    • Dear Lori,

      We suggest you bring up those topics with your prescribing doctor, as well as any intention of cutting back on the dosage, or any changes to the prescribed dosage. We thank you for the information, but please do go and report it to your physician!



  5. Hi I was prescribed 37.5 of Phentermine. On my bottle says Phentermine. No generic brand. I started today @845am. I feel nothing. No appetite suppressant. Help!

    • 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.



  6. Hi I take phentermine as well I take 2 in the morning after breakfast and 2 right after lunch both 37.5 mg I have a really high tolerance so I upped my dosage is it dangerous for me to be taking so much at a time? Plus I only take it q.i.d when I feel it’s needed if not I take it T.I.D

    • Dear Luciana,

      Phentermine is a controlled substance, and for that reason alone it’s very important to follow your doctor’s prescription on how you take it. It is natural for your body to build resistance to a drug, but you are not supposed to just increase the dosage to keep up with your resistance, for a variety of reasons. For starters, the Phentermine treatment is meant to be a short-term one. Phentermine has a very real addiction potential. This also means a withdrawal process that could make it difficult for you to stop the treatment. Taking it in greater dosages or over longer periods of time than prescribed can have other long-lasting effects upon your body.

      Please consult with your prescribing doctor about the steps to take in regards to your phentermine treatment.



  7. I\’ve been taking the 37.5 since October and have now lost 30 lbs! I was wearing a size 20 jeans now I\’m in a 14 and feel awesome!! I\’m 5\’11\” and 192 lbs currently…ALMOST TO MY GOAL…THANK YOU FOR THIS WONDERFUL PRODUCT!!!

  8. I really enjoyed while reading your article, the information you have delivered in this post was damn good. Keep sharing your post with efficient news.

  9. I started the 37.5 dose three weeks ago and experienced dizziness and panic attacks. I took for one week loosing 6 pounds and also an ER visit for a severe panic attack. While on this I ate half portions of my salads and supper. I was running 5-6 times a week with great energy. Do you think I could try just a half dose or not ever try again since I experienced that? Help!

    • Hi Nikki! We would recommend discussing this with your doctor. He or she knows your medical history best and could best determine if the downsides of phentermine could be alleviated by a lower dose, or if your negative reaction to this medication was too severe to take the chance again. In the event that you two decide that phentermine is not right for you, there are a variety of other weight loss options – including other medications or special diets. We would suggest asking your doctor about these as well 🙂 Best wishes!

  10. Great job on the site.Your content helped me a lot to take my doubts, thank you very much.

  11. The first time I was on Phentermine I was 17 and in high school and I had the same problem. I had the worst headache I had ever had in my life and my primary doctor (not the doctor who prescribed it) thought it was just a migraine, then when it wouldn\’t go away they thought I had a brain tumor, when that came back negative, I had a fever everyday for almost a week straight. I couldn\’t drive because my vision was blurry and my head hurt, and I was rushed to the hospital by ambulance. The doctor wanted to do a spinal tap until he found out I was taking Phentermine and told me to get off and stay away from it. Well, almost 4 years later I have a new doctor and she is having me try it 1 more time.

  12. Hello. I have just started taking this and I’m feeling some of the side effects but still feel kind of hungry throughout the day. It’s my 4th day taking it does this take time to kick it or is it supposed to work instantly for first time users? I’ve only been on it for a short amount of time but the Dr. made it seem like it was supposed to work instantly? Is this normal? I know everyone has different reactions to drugs but I was really relying on this to help me with my snacking throughout the day.

    • Hi H.E. – Yes, phentermine does typically work pretty quickly. If you’re still not feeling the medication’s effects, we would suggest speaking with your prescribing doctor. He or she may be able to adjust your dosage or suggest a different prescription weight loss drug to better control your appetite.

  13. Hello

    My doctor prescribed me 37.5 milligram tablets, she has me taking 1 tablet and a half daily. She states I can take up to two tablets daily but I have t yet. Unfortunately, I don’t sleep well when taking the meds and I have gained weight from snacking at night. Any suggestions. I do exercise 30 to1 hour a day, but light exercise such as walking and stationery bike due to a disability. Thank you.

    • Hi Lynn, thanks for your comment! Have you talked to your doctor about perhaps splitting one 37.5 tablet in half so that you can take part of your dose later in the day (e.g. around lunch) to better control nighttime snacking? If not, that may be a good place to start 🙂

  14. I have taken Phentermine 15 mg.capsules for two months successfully. Lost 15 pounds. The 15 mg. does not seem to be effective now. My doctor said I could take two capsules (at once) now for the final 10 pounds I need to lose. But 30 mg. makes me feel wired. Could I take one capsule and half of the powder of another capsule–1 1/2 capsules? It would still be under 30 mg. I take the yellow and dark grey capsules imprinted with \”K26.\” Thanks.

    • Hi Ann, thanks for your comment! It is not recommended to split capsules. If you’re not comfortable with your new dosing instructions, we would recommend speaking with your doctor so that the two of you can work together to find a dosage that’s both effective and doesn’t make you feel uncomfortable. He or she may suggest switching from capsules to tablets, or spreading the doses out throughout the day to alleviate the wired feeling. Nonetheless, it’t important to clear these changes with your prescribing doctor before you modify your routine. Best wishes!

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