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Phentermine

Brand names: Adipex-P, Lomaira, Qsymia (with topiramate)

Phentermine is a stimulant-like appetite suppressant used short term with diet and exercise for weight loss.

Brand namesAdipex-P, Lomaira, Qsymia (with topiramate)
Type of medicineAppetite suppressant (weight loss medicine)
Prescription?Prescription
ImportantThis page is general information, not a prescription. Don't start, stop, or change a medicine without talking to your provider or pharmacist.

Overview

It's a controlled substance. Qsymia combines it with topiramate for longer-term use.

What it's used for

  • Weight loss in adults with obesity, or overweight with health problems

How to take it

  • Take it in the morning to avoid trouble sleeping.
  • It's usually used for a few weeks (phentermine alone).

Your dose depends on your health and other medicines. Always follow your prescription label, and ask your pharmacist if anything is unclear.

Side effects

Common side effects

  • Dry mouth
  • Trouble sleeping
  • Fast heartbeat
  • Nervousness
  • Constipation
Call 911Chest pain or fainting
Call your provider todayShortness of breath, swelling, or reduced exercise tolerance (rare lung pressure problem)
Call your provider todayHigh blood pressure readings

Warnings

  • Not for people with heart disease, uncontrolled high blood pressure, overactive thyroid, glaucoma, or a history of drug misuse.

Other medicines, foods, and alcohol

  • Never take within 14 days of an MAOI.
  • Other weight-loss medicines and stimulants add risk.

Tell your provider and pharmacist about every medicine, vitamin, and supplement you take.

Pregnancy and breastfeeding

Not used in pregnancy.

Missed doses, overdose, and storage

If you miss a dose

Take it as soon as you remember, unless it's almost time for your next dose. Then skip the missed dose. Don't take two doses at once.

If someone takes too much

Call Poison Control at 1-800-222-1222 or get help online at poison.org. Call 911 if the person collapses, has a seizure, has trouble breathing, or can't be woken.

Storing it

Store at room temperature, away from heat and moisture (not in the bathroom), and out of reach of children and pets.

Conditions it's used for

Sources

Last updated 2026-11-13.