Information on Phentermine and How to Use It, Precautions and Other Medications to Avoid While Taking

This first section of our medication database entry focuses on basic drug characteristics, uses and benefits, while part two covers side effects, interactions and additional information.

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Phentermine Consumer Information

PHENTERMINE

Generic Name: phentermine (FEN ter meen)

Brand Names: Adipex-P, Fastin, Ionamin, Obenix, Obephen, Oby-Cap, Oby-Trim, Panshape M, Phentercot, Phentride, Pro-Fast HS, Pro-Fast SA, Pro-Fast SR, Teramine, Zantryl

What is the most important information I should know about phentermine?

  • Use caution when driving, operating machinery, or performing other hazardous activities. Phentermine may cause dizziness, blurred vision, or restlessness, and it may hide the symptoms of extreme tiredness. If you experience these effects, avoid hazardous activities.
  • Phentermine is habit forming. You can become physically and psychologically dependent on this medication, and withdrawal effects may occur if you stop taking it suddenly after several weeks of continuous use. Talk to your doctor about stopping this medication gradually.
  • Do not crush, chew or open any "once-daily" phentermine tablets or capsules. Swallow them whole.

What is phentermine?

  • Phentermine is a sympathomimetic amine, which is similar to an amphetamine. It is also known as an "anorectic" or "anorexigenic" drug. Phentermine stimulates the central nervous system (nerves and brain), which increases your heart rate and blood pressure and decreases your appetite.
  • Phentermine is used as a short-term supplement to diet and exercise in the treatment of obesity.
  • Phentermine may also be used for purposes other than those listed in this medication guide.

Who should not take phentermine?

  • You cannot take phentermine if you
    • have heart disease or high blood pressure;
    • have arteriosclerosis (hardening of the arteries);
    • have glaucoma;
    • have taken a monoamine oxidase inhibitor (MAOI) such as isocarboxazid (Marplan), tranylcypromine (Parnate), or phenelzine (Nardil) in the last 14 days; or
    • have a history of drug or alcohol abuse.
  • Before taking this medication, tell your doctor if you have
    • problems with your thyroid,
    • an anxiety disorder,
    • epilepsy or another seizure disorder, or
    • diabetes.
  • You may not be able to take phentermine, or you may require a lower dose or special monitoring during treatment if you have any of the conditions listed above.
  • It is not known whether phentermine will harm an unborn baby. Do not take phentermine without first talking to your doctor if you are pregnant.
  • It is also not known whether phentermine passes into breast milk. Do not take phentermine without first talking to your doctor if you are breast-feeding a baby.

How should I take phentermine?

  • Take phentermine exactly as directed by your doctor. If you do not understand these directions, ask your pharmacist, nurse, or doctor to explain them to you.
  • Take each dose with a full glass of water.
  • Phentermine is usually taken once or twice a day before a meal on an empty stomach.
  • Do not take phentermine in the evening because it may cause insomnia.
  • Do not crush, chew or open any "once-daily" phentermine tablets or capsules. Swallow them whole.
  • Never take more of this medication than is prescribed for you. Too much phentermine could be very dangerous to your health.
  • Store phentermine at room temperature away from moisture and heat.

What happens if I miss a dose?

  • Take the missed dose as soon as you remember. However, if it is almost time for your next dose or if it is already evening, skip the missed dose and take only your next regularly scheduled dose. A dose taken too late in the day will cause insomnia. Do not take a double dose of this medication.

What happens if I overdose?

  • Seek emergency medical attention.
  • Symptoms of a phentermine overdose include restlessness, tremor, rapid breathing, confusion, hallucinations, panic, aggressiveness, nausea, vomiting, diarrhea, an irregular heartbeat, and seizures.

What should I avoid while taking phentermine?

  • Use caution when driving, operating machinery, or performing other hazardous activities. Amphetamine may cause dizziness, blurred vision, or restlessness, and it may hide the symptoms of extreme tiredness. If you experience these effects, avoid hazardous activities.
  • Do not take phentermine late in the day. A dose taken too late in the day can cause insomnia.

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