Phentermine (Adipex) is used as an adjunct to exercise, behavioral modification, and caloric restriction in the short-term management (a few weeks) of obesity. Phentermine therapy is indicated for patients with no underlying risk factor but a pretreatment body mass index (BMI) of 30 or greater and those with an underlying risk factor (e.g., hypertension, diabetes mellitus, hyperlipidemia) and a pretreatment BMI of 27 or greater. Body mass index is an index of a person’s weight in relation to their height.

Phentermine should not be used in combination with selective serotonin-reuptake inhibitor antidepressants (e.g., fluoxetine, fluvoxamine, paroxetine, sertraline) or monoamine oxidase (MAO) inhibitors. To help bring about and maintain loss of weight, the patient must be taught to curtail overeating and to consume a suitable diet. Phentermine also has been used for longer periods combined with fenfluramine (no longer commercially available in the US) in selected patients for the management of this condition. Such combined long-term therapy had been used widely in the 1990s in the management of obesity. However, because of accumulated data on adverse effects associated with the drugs, fenfluramine hydrochloride and its dextrorotatory isomer dexfenfluramine hydrochloride were withdrawn from the US market in 1997.

The usual adult dosage of phentermine hydrochloride is 8 mg 3 times daily, given 30 minutes before meals. Alternatively, 15 or 30 mg of phentermine as the resin complex, or 15—37.5 mg of phentermine hydrochloride, may be given as a single daily dose in the morning.

SIDE EFFECTS: Blurred vision, dizziness, dry mouth, sleeplessness, irritability, stomach upset or constipation may occur the first few days as your body adjusts to the medication. If these effects persist or become bothersome, inform your doctor. Notify your doctor if you experience chest pain, nervousness, pounding heart, difficulty urinating, mood changes, breathing difficulties or swelling while taking this medication. If this medication makes you dizzy or lightheaded, avoid driving or engaging in activities requiring alertness. If you notice other effects not listed above, contact your doctor or pharmacist.

PRECAUTIONS: Tell your doctor your complete medical history especially if you have high blood pressure, an overactive thyroid, glaucoma, diabetes or emotional problems. This medication can be habit forming and must be used with caution. 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. This medication should be used only when clearly needed during pregnancy. Discuss the risk and benefits with your doctor. This drug may be excreted into breast milk. You may have to stop nursing or stop using this drug. Consult your doctor before breast-feeding.

DRUG INTERACTIONS: Inform your doctor about all the medicines you use, (prescription and non prescription) especially if you take high blood pressure medicine or MAO inhibitors (e.g., furazolidone, linezolid, phenelzine, selegiline, tranylcypromine), or any other weight loss medicine. Avoid “stimulant” drugs that may increase your heart rate such as decongestants or caffeine. Decongestants are commonly found in over-the-counter cough-and-cold medicines. Do not start or stop any medicine without doctor or pharmacist approval.

I personally feel that appetite suppressants are not a substitute for a proper diet. Exhaust all nutritional avenues prior to trying any medication for obesity. However, if you are planning on using this medication, for maximum effects, this must be used in conjunction with a personalized diet and exercise program.

Good Luck!

Robert L. Pastore, Ph.D., CNC, CN
Senior Nutritionist at

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