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.


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


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11 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!

  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.

  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:

    • I go to doctor gahlay for weightloss

  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.

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