Phentermine is used as an appetite suppressant. It is used in conjunction with an overall diet plan to reduce weight. Phentermine is used along with diet, exercise, and behavior therapy for the short-term management of obesity

Phentermine stimulates a part of the brain called the hypothalamus. This results in a reduced appetite.

Inform your doctor about all the medicines you use, (prescription and nonprescription) especially if you take high blood pressure medicine or MAO inhibitors (e.g., furazolidone, phenelzine, selegiline, tranylcypromine) or any other weight loss medicine. Avoid "stimulant" drugs that may increase your heart rate or blood pressure such as decongestants or caffeine. Decongestants are commonly found in over-the-counter cough and cold medicine. Phentermine is a generic form of Fastin. Some medicines or medical conditions may interact with this medicine. Inform your doctor or pharmacist of all prescription and over-the-counter medicine that you are taking. Do not use this medicine if you are also taking guanadrel, guanethidine, furazolidone, fenfluramine, dexfenfluramine, or monoamine oxidase inhibitors (MAOIs). Inform your doctor of any other medical conditions, allergies, pregnancy, or breast-feeding. Use of this medicine is not recommended if you have a history of heart conditions, brain or spinal cord disorders, atherosclerosis, high blood pressure, glaucoma, or hyperthyroidism. Contact your doctor or pharmacist if you have any questions or concerns about using this medicine.

Take on an empty stomach, once daily, 30-60 minutes before breakfast. The tablet may be broken or cut in half. Do not crush or chew tablet. Because this medication may cause sleeplessness, avoid taking a dose late in the day. Take this medication as prescribed. Do not take it more often or longer than directed. Follow the directions for using this medicine provided by your doctor. Swallow whole. Do not break, crush, or chew before swallowing. Take your dose in the morning before breakfast or 2 hours after breakfast as directed by your doctor. Be sure you take your dose at least 10 to 14 hours before bedtime. Store this medicine at room temperature in a tightly-closed container, away from heat and light. If you miss a dose of this medicine, take it as soon as possible. If it is after noon, skip the missed dose and go back to your regular dosing schedule. Do not take 2 doses at once.

Tell your doctor your complete medical history especially if you have high blood pressure, an over-active thyroid, glaucoma, diabetes or emotional problems. Consult with your doctor if you think you are pregnant or before breast-feeding. Alcohol can increase unwanted side effects of dizziness. Limit alcohol use. This drug is not recommended for use in children. Consult your doctor or pharmacist for further information. Do not exceed the recommended dose or take this medicine for longer than prescribed without checking with your doctor. Exceeding the recommended dose or taking this medicine for longer than prescribed may cause serious side effects. Keep all doctor and laboratory appointments while you are using this medicine. Before you begin taking any new medicine, either prescription or over-the-counter, check with your doctor or pharmacist. Do not drive, operate machinery, or do anything else that could be dangerous until you know how you react to this medicine. Before you have any medical or dental treatments, emergency care, or surgery, tell the doctor or dentist that you are using this medicine.

For women: If you plan on becoming pregnant, discuss with your doctor the benefits and risks of using this medicine during pregnancy. It is unknown if this medicine is excreted in breast milk. Do not breast-feed while taking this medicine.

Dry mouth, sleeplessness, irritability, stomach upset or constipation may occur the first few days as your body adjusts to Phentermine. If these effects persist or become bothersome, inform your doctor. Side effects that may occur while taking this medicine include restlessness, nervousness, difficulty sleeping, or dry mouth. If they continue or are bothersome, check with your doctor. If you notice other effects not listed above, contact your doctor, nurse, or pharmacist.