Phentermine Dosages for Weight Loss: Your GoodRx Guide

Phentermine is an oral weight-loss pill. It’s also known by the brand names Adipex-P and Lomaira. Phentermine is available as oral tablets, capsules, and orally disintegrating tablets (ODTs), giving you several options to choose from.

Phentermine is a controlled substance, which means it has a risk of misuse and dependence. So it’s best to follow your prescriber’s instructions when taking it. And unlike newer weight-loss medications, phentermine is approved for short-term use — up to 12 weeks (3 months).

So, how much phentermine do people usually take for weight loss? The answer can depend on which product and form you’re prescribed. Below we review recommended phentermine dosages, including adjustments for kidney problems, how to take phentermine, and more.

What’s the typical phentermine dosage?

Phentermine is approved for short-term use in people ages 17 and older with a body mass index (BMI) of at least 30. It’s also approved for people with a BMI of at least 27 with one or more weight-related health conditions, such as high blood pressure or diabetes.

The typical phentermine dosage for weight loss usually ranges from 15 mg to 37.5 mg daily. But how much you take and how often you take it can depend on the specific product and form. It’s also recommended to take the lowest effective dose. So, your dose may be adjusted based on how you respond to the treatment.

Phentermine is available as an oral tablet, capsule, and ODT. Most forms are usually taken once daily. It’s best to take your dose in the morning, since taking it in the evening can keep you awake at bedtime. Other forms, like Lomaira, are taken 3 times daily before meals. In this case, try to take your last dose earlier in the evening to avoid trouble falling asleep.

Phentermine tablets

• Adipex-P and generic (37.5 mg tablets): The typical phentermine dosage is 37.5 mg by mouth once daily either before breakfast or 1 to 2 hours after breakfast. This dosage may be adjusted to 18.75 mg (one-half tablet) once or twice daily, based on your individual situation.

• Lomaira (8 mg tablets): The typical dosage is 8 mg by mouth 3 times a day 30 minutes before meals. Some people may only need 4 mg (one-half tablet) at some or all of their dose times.

Phentermine capsules

• Adipex-P and generic (37.5 mg capsules): The typical dosage is 37.5 mg by mouth once daily either before breakfast or 1 to 2 hours after breakfast.

• Generic (15 mg and 30 mg capsules): The typical dosage is 15 mg to 30 mg once daily, taken 2 hours after breakfast.

Phentermine orally disintegrating tablets (ODTs)

• Generic (15 mg, 30 mg, and 37.5 mg ODTs): The typical dosage is one ODT dissolved on top of the tongue once daily in the morning. When taking your dose, make sure your hands are dry before handling the ODT. Place the tablet immediately on top of the tongue so it dissolves. Then, swallow with or without water after it dissolves.

Are there any dosage adjustments for medical conditions?

Since it’s a controlled substance, it’s best to take the lowest effective dose of phentermine. And for some people, there are factors that warrant a lower dosage than usual. This includes your age and kidney function.

Older adults

In general, older adults tend to be more sensitive to medications. There’s also a higher likelihood of health conditions that may affect how your body processes them. If you’re 65 or older, your prescriber may suggest starting with a lower phentermine dosage.

Kidney problems

Phentermine is removed from the body, in part, by the kidneys. So if you have kidney damage, you may need a lower phentermine dosage. Otherwise, phentermine could build up in your body and increase your risk of side effects.

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If you have mild or moderate kidney damage, you may not need a dosage adjustment. But if you have severe kidney damage, your phentermine dosage shouldn’t go higher than 15 mg daily. Lomaira should be taken with caution. Phentermine isn’t recommended if you have end-stage kidney disease.

What happens if you miss a dose of phentermine?

If you miss a dose of phentermine, take it as soon as you remember. But if it’s close to your next scheduled dose, or if it’s late in the evening, skip the missed dose. Then take your next scheduled dose at the usual time. Don’t take a double or extra dose to make up for a missed dose. If you do, there’s a higher risk you’ll experience side effects.

What should you do if you take too much phentermine?

The maximum recommended phentermine dosage is 37.5 mg daily. If you accidentally take an extra dose or two of phentermine, reach out to your healthcare team. This is unlikely to cause serious problems. But you could experience more side effects. With direction from your healthcare team, you can usually address any mild side effects at home.

Taking too much phentermine can lead to an overdose, which is a medical emergency. You may need treatment in a hospital. Symptoms of an overdose can include tremors, confusion, and a rapid heart beat. In serious cases, coma, hallucinations, and death could be possible. 

If you or someone you know takes a large amount of phentermine, seek immediate emergency medical care or call Poison Control at 1-800-222-1222 for guidance.

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Written by:

Austin Ulrich, PharmD, BCACP

Austin Ulrich, PharmD, BCACP, is a board-certified ambulatory care clinical pharmacist. In his early career, he provided direct patient care in a variety of settings, including hospital and community pharmacies, and in a primary care clinic as a clinical pharmacist.

Edited by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

Reviewed by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

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