Anorectic Drugs: Use in General Practice

Summary

The treatment of obesity is one of the major measures available today in the field of preventive medicine. In particular, the coronary epidemic of Western civilisation would be halted, and most cases of maturity-onset diabetes prevented, if obesity were to be treated effectively.

Anorectic drugs act mainly on the satiety centre in the hypothalamus to produce anorexia. They also have various metabolic effects involving fat and carbohydrate metabolism, but many of these may be secondary to loss of weight. Most of the drugs are related directly or indirectly to amphetamine and in addition act by increasing general physical activity. Anorectic drugs tend to lose their effect after some months, and part of this reduction in effect may be due to chemical alterations produced by the drugs in the brain. All the drugs, with the exception of fenfluramine, have a stimulant effect on the central nervous system in some individuals, resulting in restlessness and nervousness, irritability and insomnia. Fenfluramine commonly produces drowsiness in normal doses, but has stimulant effects with overdosage. Dexamphetamine, phenmetrazine and benzphetamine all tend to cause euphoria and the risk of addiction is therefore considerable. Euphoria occasionally occurs with diethylpropion, phentermine and chlorphentermine, but to a much lesser extent.

Side-effects also occur due to sympathetic stimulation and gastro-intestinal irritation. These side-effects may cause some individuals to stop taking the drug, but are never serious or dangerous. Drug interactions may occur with monoamine oxidase inhibitors and to a clinically unimportant extent, with antihypertensive drugs.

The anorectic drugs have a very definite part to play in the treatment of obesity, mainly for those individuals who have altered their eating habits but have come to a plateau of weight which they find difficult to get below. The drugs are best given in a long-acting form and can safely be continued as long as weight loss persists, provided that the clinician exercises careful supervision. Dexamphetamine, phenmetrazine and benzphetamine should rarely be used because of the danger of addiction, and chlorphentermine is potentially hazardous for long-term use. Diethylpropion emerges as the drug of first choice, as fenfluramine has a tendency to cause depression and has a higher incidence of side-effects. Fenfluramine is mainly useful for people who are especially tense and for obese maturity-onset diabetics who have been unable to lose weight with the biguanides. Mazindol and phentermine appear to be useful as alternative drugs.