Medically Reviewed by Dr. Harshi Dhingra, M.D.

Last Reviewed: Sep 06, 2022

Side Effects

Phentermine Side Effects

Possible side effects of phentermine are listed below. Tell your doctor if these side effects are severe or do not go away in a few days.

  • Unpleasant taste
  • Dry mouth
  • Diarrhea
  • Vomiting
  • Constipation
  • Dizziness
  • Headache 
  • Changes in sex drive

Rarely, more serious side effects of phentermine can occur and require immediate medical attention. Call your doctor without delay or seek emergency medical care if you experience the following symptoms:

  • Increased blood pressure
  • Heart palpitations
  • Restlessness
  • Tremors (shakiness)
  • Insomnia (trouble sleeping)
  • Chest pain
  • Shortness of breath
  • Swelling of the lower legs and ankles
  • Decreased ability to exercise compared to previously

The above list may not include all the potential adverse effects of phentermine. Contact your healthcare professional if your side effects are unusual or severe or they do not get better over time. You can also report unusual side effects to the Food and Drug Administration at 1-800-FDA-1088.

Phentermine Overdose: In case of an accidental or intentional overdose of phentermine, call your doctor immediately. You can also call the local poison control center or national poison control center at 1-800-222-1222. If a person cannot be awakened, has trouble breathing, has collapsed, or has had a seizure, call 911. 

Source: FDA