Phentermine side effects

Phentermine is available as an immediate-release and a sustained-release product. In conjunction with a healthy lifestyle, 30 to 37.5 mg of phentermine is administered once daily, typically before breakfast or 1 to 2 hours following the morning meal. The dosage should be individualized some patients maybe managed adequately at 15 to 18.75 mg daily, whereas a dose of 18.75 mg twice daily may be used to minimize side effects, excluding insomnia. To lessen the risk of insomnia, dosing phentermine in the evening should be avoided. Timed-release preparations of phentermine are not recommended because phentermine s half-life is approximately 20 hours.39... 

Figure 4.1 The chemical structure of amphetamine and fenfluramine are illustrated here. Fenfluramine (bottom) is a diet pill that is very similar in structure to amphetamine (top). Fenfluramine is an appetite suppressant, like amphetamine, but it does not have stimulant effects. Fenfluramine was proposed as a safer alternative to amphetamine and was very effective in causing weight loss, especially when used in combination with phentermine. Unfortunately, fenfluramine eventually led to devastating side effects, which led to its being withdrawn from the U.S. market.

The newest appetite suppressant, sibutramine (Meridia), works by blocking the reuptake of both serotonin and norepinephrine. It does not stimulate nerve cells to release serotonin, as do fenfluramine and dexfenfluramine. Administered at 20 mg/ day, sibutramine effectively reduces weight in obese patients, but its use has not been assessed in eating disorder patients. The most common side effects of this medication are insomnia, dry mouth, and constipation. It has not been associated with the more serious heart and lung complications observed with fenfluramine and dexfenfluramine. Because sibutramine acts in part through modulation of norepinephrine, there is no rational basis for coadministering phentermine, which acts via this same mechanism. 

New pharmacological treatments have been developed for the treatment of obesity. These include the combination of phentermine and fenfluramine (phen-fen) and, alternatively, dexfenfluramine (Redux). Phentermine (Fastin, lonamin) is a stimulant and fenfluramine (Pondimin) is a serotonin agonist. In combination they have persistent appetite suppression and weight loss effects. These medications can cause anxiety and insomnia and must be used with extreme caution if taken with antidepressants, especially SSRIs. Dexfenfluramine works similarly, but avoids the side effect of increased anxiety, and instead tends to cause diarrhea, dry mouth, and somnolence. There have also been reports of pulmonary hypertension, a potentially fatal condition, especially when taken for longer than three months. Some researchers (Ricuarte et al. 1991 McCann et al. 1994) have expressed concern because rats given these medications showed evidence of neuronal toxicity. Thus, they are effective medications, but must be used with caution. 

Side effects are those expected of any sympathomimetic agent dry mouth, palpitations and insomnia. Phentermine has an excellent safety record with a low potential for dependency. This is lowered even further with intermittent administration. 

Diethylproprion is a diphenylethylamine compound which promotes the release of noradrenaline (and to lesser extent, dopamine) from presynap-tic neurones. It was introduced into clinical practice for the treatment of obesity over 40 years ago. A number of clinical trials have shown it to be significantly more effective than placebo, although less effective than phentermine or mazindol, in helping obese patients lose weight. As noted above, it does not lead to tolerance. Side effects are mild. Some patients experience mild stimulant symptoms and tachycardia. The risk of dependence has proved to be low. 

The principal side effects of phentermine are insomnia, restlessness, and euphoria. Some patients rapidly develop toleranee to this agent, resulting in discontinuation of therapy. The combination of phentermine with fenfluramine or dexfenfluramine was as-soeiated with inereased incidences of both primary pulmonary hypertension (PPH) and ear-diae valvulopathy, but it is unlikely that phentermine alone causes these same problems. Phentermine, nonetheless, contains a warning label listing PPH and cardiac valve lesions as possible adverse events. 

Nevertheless, phentermine, from SmithKUneBeecham, became the first appetite suppressant (anorectic), which was approved by the FDA in 1959 (Fig. 5.106). [243] Phentermine leads to increased release of catecholamines like dopamine, adrenaline (epinephrine) and noradrenaline (norepinephrine), which reduce the sensation of hunger. However, the effect declines in the course of several weeks. Due to grave side-effects (sleeplessness, nervousness, nausea, obstipation. Angina pectoris problems and acute psychoses) the drug has meanwhile been withdrawn from a number of markets. 

A number of compounds act either to suppress the activity of the hunger centre in the hypothalamus or to stimulate the satiety centre. Sometimes this is an undesirable side-effect of drugs used to treat disease and can contribute to the undernutrition seen in chronically ill people (section 8.4). As an aid to weight reduction, especially in people who find it difficult to control their food intake, drugs that suppress appetite can be useful. Three compounds are in relatively widespread use as appetite suppressants fenfluramine (and more recently the D-isomer, dexfenfluramine), diethylpropion and mazindol. The combination of phentermine and fenfluramine was withdrawn in the 1990s, after a number of reports associating it with cardiac damage. 

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