Medically reviewed by Kaci Durbin, MD. Last updated on Apr 19, 2021.
What is Adipex-P?
Adipex-P (phentermine) is a prescription medicine similar to amphetamine. Phentermine stimulates the central nervous system (nerves and brain), which increases your heart rate and blood pressure and decreases your appetite.
Do not use Adipex-P if you are pregnant or breast-feeding a baby.
You should not use Adipex-P if you have a history of heart disease (coronary artery disease, heart rhythm problems, or congestive heart failure), previous stroke, severe or uncontrolled high blood pressure overactive thyroid, glaucoma, extreme agitation or nervousness, a history of drug abuse, or if you take other diet pills.
Do not use this medicine if you have used an MAO inhibitor in the past 14 days, such as isocarboxazid, linezolid, phenelzine, rasagiline, selegiline, or tranylcypromine, or if you have received a methylene blue injection. A dangerous drug interaction could occur.
Rare cases of a condition called pulmonary hypertension as well as heart valve disease have been reported in patients taking Adipex-P. Stop Adipex-P immediately if you develop difficulty breathing or shortness of breath, feelings of lightheadedness like you might faint, swelling in your legs, chest pain, or fast heartbeat.
Before taking this medicine
You should not use Adipex-P if you are allergic to phentermine, or if you have:
a history of heart disease (coronary artery disease, heart rhythm problems, congestive heart failure, stroke);
severe or uncontrolled high blood pressure;
extreme agitation or nervousness;
a history of drug abuse; or
if you take other diet pills.
Do not use Adipex-P if you have used an MAO inhibitor in the past 14 days. A dangerous drug interaction could occur. MAO inhibitors include isocarboxazid, linezolid, phenelzine, rasagiline, selegiline, tranylcypromine, methylene blue injection and others.
Do not use Adipex-P if you are pregnant. Tell your doctor right away if you become pregnant during treatment.
You should not breast-feed while using Adipex-P.
To make sure Adipex-P is safe for you, tell your doctor if you have:
heart disease or coronary artery disease;
a heart valve disorder;
high blood pressure;
anxiety or nervousness;
previous drug abuse;
diabetes (your diabetes medication dose may need to be adjusted); or
Adipex-P is not approved for use by anyone younger than 16 years old.
How should I take Adipex-P?
Take Adipex-P exactly as prescribed by your doctor. Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose.
Adipex-P 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.
Adipex-P 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 phentermine 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 this medicine 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.
Usual Dose for Obesity (Adults and Children Aged 17 and Older):
15 to 37.5 mg orally once a day before breakfast or 1 to 2 hours after breakfast.
Adipex-P should be used only for a short-term period. It should be used as part of a complete weight reduction program that includes dietary changes, exercise, and other behavioral changes.
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 Adipex-P 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 to avoid
Avoid driving or hazardous activity until you know how phentermine will affect you. Your reactions could be impaired.
Drinking alcohol with this medicine can cause side effects. Do not drink alcohol while using Adipex-P.
Adipex-P side effects
Get emergency medical help if you have signs of an allergic reaction to Adipex-P: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Call your doctor at once if you have:
feeling short of breath, even with mild exertion;
chest pain, feeling like you might pass out;
swelling in your ankles or feet;
pounding heartbeats or fluttering in your chest;
unusual changes in mood or behavior; or
Common Adipex-P side effects may include:
dry mouth, unpleasant taste;
diarrhea, constipation, stomach pain;
increased or decreased interest in sex.
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.
What other drugs will affect Adipex-P?
Taking Adipex-P together with other diet medications such as fenfluramine (Phen-Fen) or dexfenfluramine (Redux) can cause heart valve problems or a rare fatal lung disorder called pulmonary hypertension. Do not take Adipex-P with any other diet medications without your doctor's advice.
Many drugs can interact with Adipex-P. Tell your doctor about all your current medicines and any you start or stop using, especially:
Other weight loss medications;
Antidepressant medications, including MAO-inhibitors (isocarboxazid, linezolid, phenelzine, rasagiline, selegiline, tranylcypromine, methylene blue injection, and others) or selective serotonin reuptake inhibitors (fluoxetine, fluvoxamine, paroxetine, sertraline, others);
Medications for diabetes (including insulin, metformin, others); or
Certain blood pressure medications (labetalol, metoprolol, propranolol, doxazosin, prazosin, terazosin, others).
Other drugs, including prescription and over-the-counter medicines, vitamins, and herbal products, may interact with Adipex-P. Not all possible interactions are listed here. Tell your doctor about all your current medicines and any medicine you start or stop using.
Frequently asked questions
More about Adipex-P (phentermine)
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Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use Adipex-P only for the indication prescribed.
Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.
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