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.

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

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

You should not breast-feed while using phentermine.

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

• a history of heart disease (coronary artery disease, heart rhythm problems, congestive heart failure, 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.

• heart disease or coronary artery disease;
• a heart valve disorder;
• high blood pressure;
• diabetes (your diabetes medication dose may need to be adjusted); or
• kidney disease.

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.

Tell your doctor if you have ever had:

Use Fastin (Oral) exactly as directed on the label, or as prescribed by your doctor. Do not use in larger or smaller amounts or for longer than recommended.

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

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;
• tremors, feeling restless, trouble sleeping;
• unusual changes in mood or behavior; or
• increased blood pressure--severe headache, blurred vision, pounding in your neck or ears, anxiety, nosebleed.

• itching;
• dizziness, headache;
• dry mouth, unpleasant taste;
• diarrhea, constipation, stomach pain; or
• increased or decreased interest in sex.

Common side effects 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.

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.