Comparison of amphetamine sulphate and caffeine citrate in man

Summary Ten male volunteer subjects were administered single doses of one of the following compounds on five successive weekly occasions using a fully balanced design: 5 mg and 10 mg of amphetamine sulphate, 300 mg and 600 mg of caffeine citrate and lactose placebo. Two hours after ingestion subjective estimations of several mood attributes were made using graphic rating scales. The palmar skin conductance (sweat gland activity) and pulse rate were recorded during the presentation of twenty identical auditory stimuli consisting of one sec 1 kHz tones of 100 dB intensity, the interval between the tones varying randomly from 45 to 80 sec.The rate of diminution of the skin conductance responses to the repeated stimuli (habituation rate) was slowed by both drugs. The number of spontaneous fluctuations in the skin conductance tracing was increased by both drugs. Sloperatio bioassays were computed for both these variables which were then combined in a discriminant-function analysis to increase the precision of the assay. Pulse rate was elevated by amphetamine but not by caffeine.The subjective effects of the drugs were complicated because one subject demonstrated a paradoxical response to amphetamine being relaxed, drowsy and slow while under its influence.Some problems in comparisons of psychopharmacological agents in normal humans are discussed in the light of the results obtained.