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Adipex-P

Generic name: phentermineFEN-ter-meen ]
Brand names: Adipex-P, Lomaira, Suprenza
Drug classes: Anorexiants, CNS stimulants

Medically reviewed by Drugs.com on Jul 27, 2023. Written by Cerner Multum.

What is phentermine?

Phentermine is similar to an amphetamine. Phentermine stimulates the central nervous system (nerves and brain), which increases your heart rate and blood pressure and decreases your appetite.

Phentermine is used together with diet and exercise to treat obesity, especially in people with risk factors such as high blood pressure, high cholesterol, or diabetes.

Phentermine may also be used for purposes not listed in this medication guide.

Phentermine side effects

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Adipex-P may cause serious side effects. Call your doctor at once if you have:

Common side effects of Adipex-P may include:

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Warnings

You should not use this medicine if you have glaucoma, overactive thyroid, severe heart problems, uncontrolled high blood pressure, advanced coronary artery disease, extreme agitation, or a history of drug abuse.

Do not use this medicine if you have used an MAO inhibitor in the past 14 days, such as isocarboxazid, linezolid, methylene blue injection, phenelzine, rasagiline, selegiline, or tranylcypromine.

Before taking this medicine

You should not use phentermine if you are allergic to it, or if you have:

Do not use phentermine if you have used an MAO inhibitor in the past 14 days. A dangerous drug interaction could occur. MAO inhibitors include isocarboxazid, linezolid, methylene blue injection, phenelzine, rasagiline, selegiline, tranylcypromine, and others.

Weight loss during pregnancy can harm an unborn baby, even if you are overweight. Do not use phentermine if you are pregnant. Tell your doctor right away if you become pregnant during treatment.

You should not breast-feed while using phentermine.

Tell your doctor if you have ever had:

Phentermine is not approved for use by anyone younger than 16 years old.

How should I take phentermine?

Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose. Use the medicine exactly as directed.

Phentermine is usually taken before breakfast, or 1 to 2 hours after breakfast. Follow your doctor's dosing instructions very carefully.

Never use phentermine in larger amounts, or for longer than prescribed. Taking more of this medication will not make it more effective and can cause serious, life-threatening side effects.

Phentermine is for short-term use only. The effects of appetite suppression may wear off after a few weeks.

Phentermine may be habit-forming. Misuse can cause addiction, overdose, or death. Selling or giving away this medicine is against the law.

Call your doctor at once if you think this medicine is not working as well, or if you have not lost at least 4 pounds within 4 weeks.

Do not stop using phentermine suddenly, or you could have unpleasant withdrawal symptoms. Ask your doctor how to safely stop using this medicine.

Store at room temperature away from moisture and heat. Keep the bottle tightly closed when not in use.

What happens if I miss a dose?

Take the medicine as soon as you can, but skip the missed dose if it is late in the day. Do not take two doses at one time.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose of phentermine can be fatal.

Overdose symptoms may include confusion, panic, hallucinations, extreme restlessness, nausea, vomiting, diarrhea, stomach cramps, feeling tired or depressed, irregular heartbeats, weak pulse, seizure, or slow breathing (breathing may stop).

What should I avoid while taking phentermine?

Avoid driving or hazardous activity until you know how this medicine will affect you. Your reactions could be impaired.

Drinking alcohol with this medicine can cause side effects.

What other drugs will affect phentermine?

Taking phentermine together with other diet medications such as fenfluramine (Phen-Fen) or dexfenfluramine (Redux) can cause a rare fatal lung disorder called pulmonary hypertension. Do not take phentermine with any other diet medications without your doctor's advice.

Many drugs can affect phentermine. This includes prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible interactions are listed here. Tell your doctor about all your current medicines and any medicine you start or stop using.

Popular FAQ

Fatigue or tiredness can come as a result of sleepless nights or following a period of over-stimulation, however, adverse effects of phentermine also include drowsiness, fatigue, and reduced energy levels. If you’re feeling fatigued or lacking in energy while taking phentermine and the problem persists, you should consult your doctor as it may be that you have an undiagnosed medical condition.

Phentermine is safe to use when taken as prescribed by your doctor. Make sure your doctor knows about all of the other medicines you take, as well as any medical problems you have. It should not be taken along with other weight loss drugs. Though rare, high blood pressure has been reported in some patients.

Phentermine should not be taken if:

  • You have cardiovascular disease
  • You are taking or recently stopped taking drugs known as monoamine oxidase inhibitors
  • You have hyperthyroidism
  • You have glaucoma
  • You have a history of drug abuse or agitation
  • You are pregnant or nursing
  • You are sensitive to or had a reaction to other stimulant drugs

Phentermine should be prescribed as part of a weight loss plan that also includes exercise, modifying behavior and reducing calories. Phentermine is usually taken for 12 weeks or less. Weight loss effects depend on the dose of phentermine taken, as well as diet, exercise and other factors.

Phentermine stays in your system for approximately 4 days after you take it. It takes about 20 hours for half of the drug to leave your system. Many things affect how long it takes a drug to leave your system. These include your age, diet, how well your kidneys and liver are working and other factors.

Take phentermine as directed by your doctor. It is usually taken first thing in the morning, before breakfast. It may also be taken 1 to 2 hours after eating breakfast. Phentermine is not usually taken at night because it can cause insomnia.

Phentermine is a drug approved for weight loss as part of a regimen of exercise, calorie restriction and behavior modification. Phentermine may be prescribed for short-term treatment in people who have a body mass index (BMI) of 30 kg/m2 or greater. It may also be prescribed to people who have a BMI of 27 kg/m2 or greater with other risk factors, such as high blood pressure, diabetes or high cholesterol.

Some of the adverse effects of phentermine may include:

  • Heart palpitations
  • Raised blood pressure
  • A feeling of restlessness
  • Headaches
  • Dry mouth
  • Diarrhea
  • Constipation
  • Hives
  • A higher or lower libido

Phentermine affects the brain’s neurotransmitters. It is thought to cause weight loss by suppressing appetite. The exact way phentermine works to cause weight loss is not known. Phentermine belongs to the class of drugs known as sympathomimetic amines. These are more commonly known as stimulant drugs.

Phentermine is a stimulant that is chemically like amphetamine and carries a risk of dependence and abuse, which is why it is a controlled substance and only available on prescription. But the potential for dependence and abuse is lower with phentermine than other stimulants, such as amphetamine, methylphenidate, or narcotics, which is why it is a Schedule 4 controlled substance, rather than being in a higher schedule class, such as schedule 2 or 3. Continue reading

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.