The first study to directly compare the effects of ethanol and marijuana was conducted by Jones and Stone (1970). Participants who claimed a history of heavy marijuana use were administered cannabis orally or in a cigarette, and in separate sessions, they were given ethanol. The authors reported cannabis significantly increased pulse, time estimation, and low-voltage, high-frequency EEG activity. Ethanol, on the other hand, was observed to only decrease subjective time estimation. The opposing effects of ethanol and cannabis on the subjective experience of time have been demonstrated elsewhere (Tinklenberg et al., 1976), but other studies have reported that acute ethanol intoxication has either no effect on time estimation (Heishman et al., 1997) or produces a lower magnitude overestimation similar to that of cannabis (Bech et al., 1973). Importantly, Jones and Stone (1970) reported that participants who claimed a history of heavy marijuana use were less intoxicated by ethanol and showed fewer ethanol-induced neuropsychological impairments than were found in previous studies. Although, this study did not include non-cannabis using control subjects, these results led the authors to suggest that prior heavy marijuana use may convey cross-tolerance to some of the acute effects of ethanol.
