Phentermine is used as part of a short-term plan, along with a low calorie diet, for weight reduction. It is used in obese patients who have not been able to lose weight with diet and exercise alone. Phentermine belongs to the group of medicines known as appetite suppressants.

This medicine is available only with your doctor's prescription.

Take this medicine only as directed by your doctor. Do not take more of it, do not take it more often, and do not take it for a longer time than your doctor ordered. If you take too much of this medicine, it may become habit-forming (causing mental or physical dependence).

This medicine is available in four forms: capsules, disintegrating tablets, extended-release capsules, and tablets. Carefully follow the dosing instructions for the form you are using.

Swallow the extended-release capsule whole. Do not crush, break, or chew it.

Take the disintegrating tablet with or without food. Make sure your hands are dry before touching the tablet. Place the tablet on the top of your tongue right after removing it from the bottle. It should melt quickly. After the tablet has melted, swallow or take a sip of water.

Swallow the tablet whole. Do not crush, break, or chew it.

Carefully follow your doctor's instructions for a reduced-calorie diet plan and regular exercise. Talk with your doctor before starting an exercise program.

To avoid trouble with sleeping, take the last dose of the day about 4 to 6 hours before bedtime, unless your doctor tells you otherwise.

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur:

Rare

Seeing, hearing, or feeling things that are not there

severe mental changes

Incidence not known

Chest pain

decreased ability to exercise

dizziness

fainting

fast, irregular, pounding, or racing heartbeat or pulse

headache

numbness or tingling in the arms or legs

swelling of the feet or lower legs

trembling or shaking of the legs, arms, hands, or feet

trouble breathing

trouble with thinking, speaking, or walking

weakness

Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Incidence not known

Decreased interest in sexual intercourse

difficulty having a bowel movement (stool)

dry mouth

false or unusual sense of well-being

hives or welts, itching, or skin rash

inability to have or keep an erection

increased in sexual ability, desire, drive, or performance

increased interest in sexual intercourse

loss in sexual ability, desire, drive, or performance

redness of the skin

unpleasant taste

Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

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

It is very important that your doctor check your progress at regular visits to make sure that this medicine is working properly and does not cause any unwanted effects.

Do not use phentermine if you are also using similar medicines such as benzphetamine, diethylpropion, mazindol, phendimetrazine, Bontril®, or Didrex®. Do not use this medicine if you also take an MAO inhibitor (MAOI), such as isocarboxazid (Marplan®), phenelzine (Nardil®,), selegiline (Eldepryl®), or tranylcypromine (Parnate®), or if you have used an MAOI within the past 14 days. Using these medicines together may cause serious unwanted effects.

Using this medicine while you are pregnant can harm your unborn baby. Use an effective form of birth control to keep from getting pregnant. If you think you have become pregnant while using this medicine, tell your doctor right away.

This medicine may be habit-forming. If you think this medicine is not working properly after you have taken it for a few weeks, do not increase the dose. Instead, check with your doctor.

Call your doctor right away if you notice a decrease in your ability to exercise, or if you faint, have chest pain, swelling of your feet or lower legs, or trouble with breathing. These may be symptoms of a very serious heart or lung problem.

This medicine may cause some people to become dizzy, lightheaded, or less alert than they are normally. Make sure you know how you react to this medicine before you drive, use machines, or do anything else that could be dangerous if you are dizzy or not alert.

This medicine may affect blood sugar levels. Diabetic patients may notice a change in blood or urine sugar tests. Check with your doctor if you have any questions.

Avoid drinking alcohol while you are using this medicine.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription and nonprescription (over-the-counter) medicines, dietary supplements, herbal remedies, or medicines for appetite control, asthma, colds, cough, hay fever, and sinus problems.