Amphetamines are non-catecholamine, sympathomimetic amines with CNS stimulant activity. Peripheral actions include elevations of systolic and diastolic blood pressures, and weak bronchodilator, and respiratory stimulant action.
Amphetamine, as the racemic form, differs from dextroamphetamine in a number of ways. The l-isomer is more potent than the d-isomer in cardiovascular activity, but much less potent in causing CNS excitatory effects. The racemic mixture also is less effective as an appetite suppressant when compared to dextroamphetamine. There is neither specific evidence which clearly establishes the mechanism whereby amphetamines produce mental and behavioral effects in children, nor conclusive evidence regarding how those effects relate to the condition of the central nervous system.
Drugs in this class used in obesity are commonly known as "anorectics" or "anorexigenics." It has not been established, however, that the action of such drugs in treating obesity is primarily one of appetite suppression. Other central nervous system actions or metabolic effects, may be involved, for example. Adult obese subjects instructed in dietary management and treated with "anorectic" drugs lose more weight on the average than these treated with placebo and diet, as determined in relatively short-term clinical trials.
The magnitude of increased weight loss of drug-treated patients over placebo-treated patients is only a fraction of a pound a week. The rate of weight loss is greatest in the first weeks of therapy for both drug and placebo subjects and tends to decrease in succeeding weeks. The origins of the increased weight loss due to the various possible drug effects are not established. The amount of weight loss associated with the use of an "anorectic" drug varies from trial to trial, and the increased weight loss appears to be related in part to variables other than the drug prescribed, such as the physician-investigator, the population treated, and the diet prescribed. Studies do not permit conclusions as to the relative importance of the drug and nondrug factors on weight loss.
The natural history of obesity is measured in years, whereas the studies cited are restricted to few weeks duration; thus, the total impact of drug-induced weight loss over that of diet alone must be considered clinically limited.
