Phentermine is a stimulant that is similar to an amphetamine. Phentermine is an appetite suppressant that affects the central nervous system.

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

Phentermine may also be used for purposes other than those listed in this medication guide.

Take this medication exactly as it was prescribed for you. Do not take the medication in larger amounts, or take it for longer than recommended by your doctor. Follow the directions on your prescription label.

Taking high doses of phentermine over long periods of time can cause severe skin problems, sleep problems (insomnia), personality changes, and feeling hyperactive or irritable.

Take this medicine with a full glass of water.

It is best to take phentermine on an empty stomach before breakfast, or at least 10 to 14 hours before bedtime.

Phentermine should be taken only for a short time, such as a few weeks.

Do not crush, chew, break, or open an extended-release capsule. Swallow the pill whole. It is specially made to release medicine slowly in the body. Breaking or opening the pill would cause too much of the drug to be released at one time.

You may have withdrawal symptoms when you stop using phentermine after using it over a long period of time. Do not stop using this medication suddenly without first talking to your doctor. You may need to use less and less before you stop the medication completely.

Do not take phentermine in the evening because it may cause sleep problems (insomnia).

Stop taking phentermine if you have increased hunger or if you otherwise think the medication is not working properly. Do not take more phentermine for an increased effect. Taking too much of this medication can cause serious, life-threatening side effects.

Phentermine may be habit-forming and should be used only by the person it was prescribed for. Keep track of how many pills have been used from each new bottle of this medicine. Phentermine is a drug of abuse and you should be aware if any person in the household is using this medicine improperly or without a prescription.

Store phentermine at room temperature away from moisture and heat.

Before taking phentermine, tell your doctor if you are using any of the following drugs:

• medicines to treat high blood pressure;

• insulin or diabetes medication you take by mouth;

• guanadrel (Hylorel), guanethidine (Ismelin);

• antidepressants such as citalopram (Celexa), escitalopram (Lexapro), fluoxetine (Prozac, Sarafem), fluvoxamine (Luvox), paroxetine (Paxil), or sertraline (Zoloft); or

• antidepressants such as amitriptyline (Elavil, Etrafon), amoxapine (Ascendin), clomipramine (Anafranil), desipramine (Norpramin), doxepin (Sinequan), imipramine (Janimine, Tofranil), nortriptyline (Pamelor), protriptyline (Vivactil), or trimipramine (Surmontil).

If you are using any of these drugs, you may not be able to use phentermine, or you may need dosage adjustments or special tests during treatment.

There may be other drugs not listed that can affect phentermine. Tell your doctor about all the prescription and over-the-counter medications you use. This includes vitamins, minerals, herbal products, and drugs prescribed by other doctors. Do not start using a new medication without telling your doctor.

Avoid drinking alcohol. It can increase some of the side effects of phentermine.

Phentermine can cause side effects that may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be awake and alert.

Seek emergency medical attention if you think you have used too much of this medication. An overdose of phentermine can be fatal.

Symptoms of a phentermine overdose may include confusion, hallucinations, feeling restless or aggressive, nausea, vomiting, diarrhea, stomach pain, irregular heartbeat, tremors, rapid breathing, confusion, hallucinations, feeling light-headed, fainting, or seizure (convulsions).

Take the missed dose as soon as you remember. If it is almost time for your next dose, skip the missed dose and take the medicine at your next regularly scheduled time. Do not take extra medicine to make up the missed dose.

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.

Phentermine can cause side effects that may impair your thinking or reactions. Be careful if you drive or do anything that requires you to be awake and alert.

Avoid drinking alcohol. It can increase some of the side effects of phentermine.

Phentermine may be habit-forming and should be used only by the person it was prescribed for. Keep track of how many pills have been used from each new bottle of this medicine. Phentermine is a drug of abuse and you should be aware if any person in the household is using this medicine improperly or without a prescription.

You may have withdrawal symptoms, such as depression and extreme tiredness, when you stop using phentermine after using it over a long period of time. Do not stop using phentermine suddenly without first talking to your doctor. You may need to use less and less before you stop the medication completely.

Do not take phentermine if you have used an MAO inhibitor such as isocarboxazid (Marplan), phenelzine (Nardil), rasagiline (Azilect), selegiline (Eldepryl, Emsam), or tranylcypromine (Parnate) within the past 14 days. Serious, life-threatening side effects can occur if you take phentermine before the MAO inhibitor has cleared from your body.

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.

Do not take this medication if you are allergic to phentermine or other stimulants, or if you have:

• heart disease or high blood pressure;

• arteriosclerosis (hardening of the arteries);

• an overactive thyroid;

• glaucoma;

• if you are in an agitated state; or

• if you have a history of drug or alcohol abuse.

Before taking phentermine, tell your doctor if you are allergic to any drugs, or if you have:

• problems with your thyroid,

• an anxiety disorder,

• epilepsy or another seizure disorder, or

• diabetes.

If you have any of these conditions, you may not be able to use phentermine, or you may need a dosage adjustment or special tests during treatment.

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 or if it could harm a nursing baby. Do not take phentermine without first talking to your doctor if you are breast-feeding a baby.

Do not give this medication to anyone younger than 16 years old without the advice of a doctor.

Your pharmacist has information about phentermine written for health professionals that you may read.

Phentermine is available with a prescription under the brand names Adipex and Fastin. Other brand or generic formulations may also be available. Ask your pharmacist any questions you have about this medication, especially if it is new to you.

• Adipex-P 37.5 mg—white, oblong, scored tablets with blue speckles

• Adipex-P 37.5 mg—light-blue-and-white capsules with two blue bands

• Fastin 30 mg—blue-and-clear capsules with blue and white beads