Phentermine is used along with a doctor-approved, reduced-calorie diet, exercise, and behavior change program to help you lose weight. It is used in people who are significantly overweight (obese) and have not been able to lose enough weight with diet and exercise alone. Losing weight and keeping it off can reduce the many health risks that come with obesity, including heart disease, diabetes, high blood pressure, and a shorter life.

It is not known how this medication helps people to lose weight. It may work by decreasing your appetite, increasing the amount of energy used by your body, or by affecting certain parts of the brain. This medication is an appetite suppressant and belongs to a class of drugs called sympathomimetic amines.

Take this medication by mouth, usually once a day 1 hour before breakfast or 1-2 hours after breakfast or as directed by your doctor. The tablet form may be taken at a lower dose (8 milligrams) up to 3 times a day 30 minutes before meals. Taking this medication late in the day may cause trouble sleeping (insomnia).

If you are using sustained-release capsules, swallow the medication whole. Do not crush or chew the sustained-release capsules. Doing so can destroy the long action of the drug and may increase side effects.

The dosage is based on your medical condition and response to therapy. Your doctor will adjust the dose to find the best dose for you. Use this medication regularly and exactly as prescribed in order to get the most benefit from it. To help you remember, take it at the same time(s) each day.

This medication is usually taken for only a few weeks at a time. It should not be taken with other appetite suppressants (see also Drug Interactions section). The possibility of serious side effects increases with longer use of this medication and use of this drug along with certain other diet drugs.

This medication may cause withdrawal reactions, especially if it has been used regularly for a long time or in high doses. In such cases, withdrawal symptoms (such as depression, severe tiredness) may occur if you suddenly stop using this medication. To prevent withdrawal reactions, your doctor may reduce your dose gradually. Consult your doctor or pharmacist for more details, and report any withdrawal reactions immediately.

Rarely, abnormal drug-seeking behavior (addiction) is possible with this medication. Do not increase your dose, take it more frequently, or use it for a longer time than prescribed. Properly stop the medication when so directed.

This medication may stop working well after you have been taking it for a few weeks. Talk with your doctor if this medication stops working well. Do not increase the dose unless directed by your doctor. Your doctor may direct you to stop taking this medication.

Dizziness, dry mouth, difficulty sleeping, irritability, nausea, vomiting, diarrhea, or constipation may occur. If these effects persist or worsen, notify your doctor or pharmacist promptly.

Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

Tell your doctor immediately if any of these unlikely but serious side effects occur: fast/irregular/pounding heartbeat, mental/mood changes (e.g., agitation, uncontrolled anger, hallucinations, nervousness), uncontrolled muscle movements, change in sexual ability/interest.

Stop taking this medication and seek immediate medical attention if any of these rare but very serious side effects occur: severe headache, slurred speech, seizure, weakness on one side of the body, vision changes (e.g., blurred vision).

This drug may infrequently cause serious (sometimes fatal) lung or heart problems (pulmonary hypertension, heart valve problems). The risk increases with longer use of this medication and use of this drug along with other appetite-suppressant drugs/herbal products. If you notice any of the following unlikely but very serious side effects, stop taking this medication and consult your doctor or pharmacist immediately: chest pain, difficulty breathing with exercise, decreased ability to exercise, fainting, swelling of the legs/ankles/feet.

A very serious allergic reaction to this drug is rare. However, seek immediate medical attention if you notice any of the following symptoms of a serious allergic reaction: rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing.

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US -

Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Before taking this medication, tell your doctor or pharmacist if you are allergic to it; or to any other sympathomimetic amines (e.g., decongestants such as pseudoephedrine, stimulants such as amphetamine, appetite suppressants such as diethylpropion); or if you have any other allergies.

This medication should not be used if you have certain medical conditions. Before using this medicine, consult your doctor or pharmacist if you have: uncontrolled high blood pressure, glaucoma, history of alcohol/drug abuse, vascular heart disease (e.g., chest pain, heart attack), mental/mood problems (e.g., severe anxiety, bipolar disorder, psychosis, schizophrenia), high blood pressure in the lungs (pulmonary hypertension), stroke, overactive thyroid (hyperthyroidism).

Before using this medication, tell your doctor or pharmacist your medical history, especially of: diabetes, controlled high blood pressure, other heart problems (e.g., heart murmur, fast/irregular heartbeat, heart valve problems), kidney disease, seizure problem.

This drug may make you dizzy or (rarely) drowsy or cause blurred vision. Do not drive, use machinery, or do any activity that requires alertness or clear vision until you are sure you can perform such activities safely. Avoid alcoholic beverages.

Before having surgery, tell your doctor or dentist that you are using this medication.

Kidney function declines as you grow older. This medication is removed by the kidneys. Therefore, elderly people may be at greater risk for dizziness and high blood pressure while using this drug.

During pregnancy, this medication should be used only when clearly needed. It is not recommended for use for long periods or in high doses near the expected delivery date because of possible harm to the unborn baby. Discuss the risks and benefits with your doctor. Infants born to mothers who have been using this medication for a long time or in high doses may have withdrawal symptoms such as irritability or extreme tiredness. Tell your doctor immediately if you notice any of these symptoms in your newborn.

This drug may pass into breast milk and could have undesirable effects on a nursing infant. Therefore, breast-feeding is not recommended while using this drug. Consult your doctor before breast-feeding.

Your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with them first.

This drug should not be used with certain medications because very serious interactions may occur. If you are taking or have taken other appetite-suppressant drugs in the past year (e.g., diethylpropion, sibutramine, ephedra/ma huang), tell your doctor or pharmacist before starting this medication.

Avoid taking MAO inhibitors (e.g., furazolidone, isocarboxazid, linezolid, moclobemide, phenelzine, procarbazine, rasagiline, selegiline, tranylcypromine) within 2 weeks before, during, and after treatment with this medication. In some cases a serious (possibly fatal) drug interaction may occur.

If you are currently using any of these medications, tell your doctor or pharmacist before starting this medication.

Before using this medication, tell your doctor or pharmacist of all prescription and nonprescription/herbal products you may use, especially: drugs for depression (e.g., TCAs such as imipramine, SSRIs and SNRIs such as paroxetine, fluoxetine, venlafaxine, duloxetine), drugs for diabetes (e.g., insulin, sulfonylureas such as glipizide), high blood pressure medicine (e.g., guanethidine, methyldopa), phenothiazines (e.g., prochlorperazine, promethazine, chlorpromazine), other stimulants (e.g., amphetamines, methylphenidate, street drugs such as cocaine or MDMA/"ecstasy").

Tell your doctor or pharmacist if you also take drugs that cause dizziness or drowsiness such as: certain antihistamines (e.g., diphenhydramine), anti-seizure drugs (e.g., carbamazepine), medicine for sleep or anxiety (e.g., alprazolam, diazepam, zolpidem), muscle relaxants, narcotic pain relievers (e.g., codeine), psychiatric medicines (e.g., risperidone, amitriptyline, trazodone).

Also report the use of drugs which might increase seizure risk when combined with this medication such as isoniazid (INH), phenothiazines (e.g., thioridazine), theophylline, or tricyclic antidepressants (e.g., amitriptyline), among others.

Check the labels on all your medicines/herbal products (e.g., cough-and-cold products containing decongestants such as pseudoephedrine, diet aids such as phenylpropanolamine, ephedra/ma huang) because they may contain ingredients that could increase your heart rate or blood pressure. Ask your pharmacist about using those products safely.

Caffeine can increase the side effects of this medication. Avoid drinking large amounts of beverages containing caffeine (coffee, tea, colas) or eating large amounts of chocolate.

This document does not contain all possible interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist.

If overdose is suspected, contact your poison control center or emergency room immediately. US residents can call the US National Poison Hotline at 1-800-222-1222. Canada residents can call a provincial poison control center. Symptoms of overdose may include: rapid breathing, unusual restlessness, fast/slow/irregular heartbeat, chest pain, hallucinations, seizures, loss of consciousness.

Appetite suppressants should not be used in place of proper diet. For best results, this drug must be used along with a doctor-approved diet and exercise program.

Do not share this medication with others. It is against the law.

Laboratory and/or medical tests (e.g., blood pressure, heart tests, kidney tests) may be performed periodically to monitor your progress or check for side effects. Consult your doctor for more details.

If you miss a dose, take it as soon as you remember. If it is near the time of the next dose or late in the evening, skip the missed dose and resume your usual dosing schedule. Do not double the dose to catch up.

Store in a tightly closed container at room temperature between 68-77 degrees F (20-25 degrees C) away from light and moisture. Keep all medications away from children and pets.

Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company for more details about how to safely discard your product.

Information last revised July 2009 Copyright(c) 2009 First DataBank, Inc.