Intravenous caffeine in stimulant drug abusers: subjective reports and physiological effects

The present study was conducted to examine the self-reported (i.e., subjective) and physiological effects of intravenous caffeine in 10 subjects with histories of stimulant drug abuse. Under double-blind conditions, subjects received each dose of caffeine (0, 37.5, 75, 150 or 300 mg/70 kg) twice according to a latin-square design; injections were 10 sec in duration and separated by at least 24 hr. Effects were measured before injection and repeatedly afterward for 60 min. Caffeine dose-dependently increased ratings of positive mood (e.g., increased ratings of drug liking and high), which peaked at 2 min after injection and progressively decreased. Caffeine also dose-dependently increased the frequency of stimulant identifications on the Pharmacological Class Identification Questionnaire (e.g., like cocaine, amphetamine). Caffeine also produced negative-mood effects (e.g., increased ratings of bad effects) and increases in self-reported desire for cocaine. In contrast to the positive-mood effects, the negative-mood effects were of smaller magnitude and only significant at the highest dose. Caffeine increased reports of unusual smells and tastes. Caffeine decreased heart rate (7 bpm) and skin temperature (4 degrees C), and increased systolic and diastolic blood pressures (8 and 6 mm Hg, respectively). The mood effects but not the physiological effects of intravenous caffeine were similar to those previously observed with cocaine in studies using similar methods and subjects. Intravenous caffeine administration may provide a useful model system for investigating factors relevant to the use and abuse of stimulant drugs.