Psychopharmacology(1993) 11t : 163 168 Psychopharmacology © Springer-Verlag 1993 Acute effects of marijuana smoking on aggressive, escape and point-maintained responding of male drug users Don R. Cherek, John D. Roache, Mark Egli, Chester Davis, Ralph Spiga, and Katherine Cowan Human Behavioral Pharmacology Laboratory, Substance Abuse Research Center, Department of Psychiatry and Behavioral Sciences, University of Texas, Health ScienceCenter at Houston, Texas 77030-3497, USA Received March 3, 1992/ Final version October 29, 1992 Abstract. Aggressive, escape and point-maintained oper- ant responding of male marijuana smokers were measured during six 25-rain sessions conducted over an 8-h experi- mental day. Aggressive responding ostensibly subtracted points exchangeable for money from another subject. Escape responding protected the subject's counter from point subtractions initiated by the other subject for some period of time. Aggressive and escape responding were engendered by subtracting points from the subjects and maintained by initiation of intervals free of point sub- tractions. Point subtractions presented to the subjects were attributed to other persons. Subjects earned points exchangeable for money on a third response option. Sub- jects participated in one session prior to smoking and five sessions after smoking. Subjects smoked placebo or three different potencies of active marijuana cigarettes. Mari- juana smoking effects on escape responding were not significant and depended upon the frequency of provoca- tion. Point-maintained responding was decreased after marijuana smoking. Aggressive responding was increased for the first hour after smoking and returned to placebo levels later in the day. These effects of marijuana smoking on aggressive responding are discussed in terms of subject characteristics, particularly drug use history. Key words: Aggression Escape - Human - Marijuana - Operant Marijuana use and criminal activity are often associated in today's society; however, critical reviews (e.g., Abel 1977) have concluded that marijuana does not induce violence in typical users. The incidence and frequency of marijuana use have been found to be higher among adolescents more frequently involved with violence, and more likely to have quit school or at high risk of doing so (Chavez et al. 1989; Watts and Wright 1990). Attributing causality to such associated factors occurring in the nat- Correspondence to: Don R. Cherek ural environment is very problematic. Most likely, envir- onmental context plays a major role in instances where marijuana smoking has been linked with violence. Laboratory studies of aggression in non-human sub- jects have reported decreased aggressive behavior follow- ing administration of A-9 tetrahydrocannabinol (THC), the active component of marijuana. Injections of THC decreased the rate of key pecking maintained by access to a stuffed target bird that could be attacked at doses that did not affect key pecking intermittently reinforced with food (Cherek and Thompson 1973). In mice, rats and squirrel monkeys, THC administration reduced the fre- quency of intruder-provoked attack behaviors in resident animals (Miczek 1978). Defense, submission, flight be- haviors and locomotor activity were frequently not sup- pressed by THC. In these experiments, THC reliably suppressed aggressive behavior with some degree of specificity. Laboratory studies of human aggression have opera- tionally defined an aggressive response as one which actually or ostensibly results in the presentation of an aversive stimulus, e.g., electric shock, to another person (Buss 1961). One study (Taylor et at. 1976) compared the effects of alcohol and oral THC doses on a competitive reaction time task. In this procedure, subjects selected shock intensities that would be presented to an opponent (a confederate) if the subject's reaction time was faster. Shocks were presented to the subjects on half of the trials. Intensities selected by the opponent increased progress- ively across trials. The aggression measure was the shock intensity selected by the subject. Subjects receiving oral THC (0.1 or 0.3 mg/kg) did not differ significantly from control subjects, although there was a tendency for sub- jects receiving the highest dose to respond in a less aggressive manner. A subsequent study (Myerscough and Taylor 1985) examined the effects of a wider range of doses (0.1, 0.25 and 0.4 mg/kg THC) on aggression using the same para- digm. Following administration of the lowest THC dose, subjects set slightly higher shock intensities for their opponents, while at higher doses no changes were ob- served. Without a placebo group, it was not possible to