Fastin Side Effects

Generic name: phentermine

Note: This document contains side effect information about phentermine. Some of the dosage forms listed on this page may not apply to the brand name Fastin.

Some side effects of Fastin may not be reported. Always consult your doctor or healthcare specialist for medical advice. You may also report side effects to the FDA.

For the Consumer

Applies to phentermine: oral capsule, oral tablet, oral tablet disintegrating

Get emergency medical help if you have any of these signs of an allergic reaction while taking phentermine (the active ingredient contained in Fastin) hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Call your doctor at once if you have a serious side effect such as:

• 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;

• confusion or irritability, unusual thoughts or behavior;

• feelings of extreme happiness or sadness; or

• dangerously high blood pressure (severe headache, blurred vision, buzzing in your ears, anxiety, chest pain, shortness of breath, uneven heartbeats, seizure).

Common side effects may include:

• feeling restless or hyperactive;

• headache, dizziness, tremors;

• sleep problems (insomnia);

• dry mouth or an unpleasant taste in your mouth;

• diarrhea or constipation, upset stomach; or

• increased or decreased interest in sex, impotence.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects.

For Healthcare Professionals

Applies to phentermine: compounding powder, oral capsule, oral capsule extended release, oral tablet, oral tablet disintegrating

Cardiovascular

Cardiovascular adverse effects may be associated with phentermine (the active ingredient contained in Fastin) Palpitations, tachycardia, elevation of blood pressure, ischemic event have been reported. Primary pulmonary hypertension and valvular heart disease has been reported in patients taking phentermine in combination with fenfluramine or dexfenfluramine and in rare cases in patients who have taken phentermine alone. Analysis of available data suggests that fenfluramine and dexfenfluramine are the causal agents, and both drugs have been withdrawn from the market as of September 15, 1997.

A 37-year-old woman was admitted to the hospital after an episode of ventricular fibrillation. The patient was being treated for moderate obesity and had been taking phentermine hydrochloride, thyroid (USP), and trichlormethiazide. Her previous medical history had been unremarkable. It was suspected that one or more of her medications contributed to the nearly fatal arrhythmia.

Two case reports describe patients using phentermine (one in combination with phendimetrazine) who later developed ischemic cerebrovascular disease. One suffered a cerebral infarct with angiographic evidence of vasculopathy involving multiple vascular beds. The other patient developed headache and a hemisensory disturbance of seven days duration.

A case of fatal pulmonary hypertension has also been reported in a 29-year-old woman 8 months following the use of fenfluramine (of which dexfenfluramine is the dextro isomer) and phentermine for only 23 days. Histopathological findings upon autopsy indicated severe pulmonary hypertension. She did not smoke and had no family history of pulmonary hypertension. No obvious risk factors other than obesity were present, although preexisting disease was not ruled out.

A case of restrictive cardiomyopathy due to endocardial fibrosis after short term use of fenteramine in combination with phentermine has been reported.

Nervous system

Phentermine (the active ingredient contained in Fastin) produces nervous system stimulation, which may result in tremor, anxiety, restlessness, dizziness, insomnia, euphoria, dysphoria, and headache.

Fifty women with refractory obesity received phentermine resinate for a period of 20 weeks. Three defaulted from the study due to incapacitating headaches without significant change in blood pressure. Two additional patients defaulted due to complaints of irritability.

A double-blind clinical trial of phentermine and fenfluramine involving 81 people with simple obesity reported several CNS complaints from patients taking phentermine resin during the study (twenty six complaints during the first 6 weeks of the study). The number of complaints diminished with time over the course of the study. Only seven complaints of CNS effects were reported at 20 weeks. Complaints reported by patients include sleep difficulties, nervousness, depression, fatigue and increased dreaming.

Psychiatric

Rarely psychotic episodes have been reported at recommended doses with some sympathomimetic drugs.

Gastrointestinal

Gastrointestinal adverse effects may include dryness of the mouth, unpleasant taste, diarrhea, and constipation.

Dermatologic

An allergic reaction resulting in urticaria may occur.

Endocrine

Endocrine effects such as impotence and changes in libido may occur in patients taking phentermine (the active ingredient contained in Fastin)

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