We describe the limitations on studying the interactions of drugs of abuse in humans. Two 'acute' studies were carried out. In the first study, the administration of alcohol/placebo with cocaine showed the possibility of identifying the euphoric effect of the drugs by the EEG power spectra analysis in terms of enhancement of alpha- and beta-wave activity. The results of the second study, in which cocaine and buprenorphine were administered, show the existence of low-dose interactions and the influence of buprenorphine on craving for cocaine.