The present study was designed to investigate the effects of social conditions (i.e., presence of others) on the acute responses to MDMA. MDMA is typically used in highly social settings such as dance parties, or raves. In laboratory animals, as well, the effects of stimulant drugs are enhanced by the presence of other conspecifics, especially other animals that are also self-administering the drug. In the present study, MDMA produced its prototypical effects of increased heart rate and positive subjective effects in all three conditions, whether participants were alone, with a research assistant, or with other drug-treated participants. We found modest evidence for an enhancement of MDMA effects when participants received the drug with other co-participants. In particular, MDMA produced greater increases in cardiovascular measures and some subjective ratings when participants were tested with co-participants. We also found that the drug influenced the perception of others: MDMA increased ratings of attractiveness of the other person and increased social interaction. Our findings suggest that social context has a modest influence on responses to MDMA.

On some measures, the influence of the presence of other participants on responses to MDMA varied across the two doses. For most of the cardiovascular and subjective measures, the effects of MDMA were dose dependent and linear, which is consistent with previous studies of the acute effects of MDMA (Bedi et al. 2010; Harris et al. 2002; Hysek et al. 2012; Kirkpatrick et al. 2014b; Tancer and Johanson 2003). However, in the OPP condition, the drug produced greater increases in heart rate at the lower dose and systolic blood pressure at the higher dose, compared to participants tested alone or with a research assistant present. The lower dose also produced greater ratings of feeling the drug and feeling dizzy in the OPP group. These data are consistent with results showing that a social context can enhance or intensify acute drug effects (de Wit et al. 1997; Doty and de Wit 1995; Evans et al. 1996; Kelly et al. 1994; Kirkpatrick and de Wit 2013). It is possible that the greater drug effects in OPP participants are related to an overall increase in activity related to social interaction. That is, the drug may increase social interaction, and the increase in social interaction may have effects on other measures. Separating these processes will be a challenge for future studies.

We observed differences in responses to MDMA in the OPP compared to the RAP group. The higher dose of MDMA produced greater feelings of confidence in the OPP group than the RAP group, and the lower MDMA dose increased ratings on feeling insightful, and drug wanting, liking, and disliking in the OPP group only. There are several possible reasons for these differences. First, they may be related to the number of individuals present in the room: in the RAP group, there was just one additional person, and in the OPP group, there were two or three. Second, they may be related to the responses to the drug in the other participants: This can only be determined in a carefully designed study where the drug state of the other co-participant is controlled (e.g., Kirkpatrick and de Wit 2013). Third, it is also possible that the participants’ knowledge that the research participant was a member of the staff —whereas the co-participants were also research volunteers—influenced participants’ responses. Although our data indicate the importance of the social context (Carlin et al. 1972; Kirkpatrick and de Wit 2013; Sher 1985), they leave open the question of which variables influence the apparent social facilitation of the drug effect.

The study also provided information about the effects of MDMA on social behavior; the drug increased both objective and subjective measures of social behavior. MDMA increased the time the participants spent interacting and talking. The larger dose of MDMA also increased ratings of attractiveness of the other person (research assistant or other participant) in all three groups of participants. Overall, these findings are consistent with data from preclinical and human studies showing that MDMA enhances social processing (Bedi et al. 2009, 2010; Hysek et al. 2012; Kirkpatrick et al. 2014a, b; Wardle and de Wit 2014) and social behavior, such as increased time spent interacting in rats (Ramos et al. 2013; Thompson et al. 2009), and increases in empathy and prosociality (Hysek et al. 2013). Surprisingly, the low dose of MDMA produced greater levels of interaction than the larger dose, whereas others have reported that lower doses of MDMA (e.g., 75 mg) produce less empathogenic effects and smaller increases in oxytocin levels than larger doses (e.g., 125 mg, Schmid et al. 2014). This nonlinear dose response on measures of social interaction remains to be investigated. The effects of MDMA on social interaction appear to be similar to effects of several other drugs, including alcohol and other stimulant drugs (Higgins and Stitzer 1988; Lindfors and Lindman 1987; Marrone et al. 2010; Stitzer et al. 1981; Ward et al. 1997). Whether specific aspects of the prosocial effects of MDMA distinguish it from other drugs remains to be determined.

The current results should be interpreted in the context of at least three limitations. First, our study was small (N = 32 across three groups), and thus we may not have had the power to detect subtler drug response differences between the groups. Second, in the OPP condition, participants were arbitrarily matched with other co-participants, based mainly on availability. It is possible that the characteristics of the partner influenced both subjective drug response and sociability. For example, it is possible that the personalities of the participants could mediate the drug experience for each individual, creating positive experiences in some and negative experiences in others. Although participants were randomly assigned participants to groups to minimize this type of bias, future studies might assess and systematically evaluate the influence of partner characteristics (i.e., friends versus strangers) on drug response. Another limitation relates to the social contexts that we created and the activities that the participants could engage in. For instance, we allowed participants to watch movies, which may have confounded the observed drug effect by influencing their mood states and altering the social interactions in a number of ways, including possibly reducing the time spent talking. Finally, our laboratory environment differs from naturalistic social contexts in which MDMA is used, and future studies might investigate the drug under more naturalistic social conditions.

In conclusion, we found modest evidence that the effects of MDMA were influenced by a social context. We found that the presence of other intoxicated participants increased cardiovascular responses and enhanced some subjective responses to MDMA. However, for the majority of measures, the groups’ drug responses did not differ meaningfully, suggesting that the social contexts used in the present study produced modest influences on drug response. Additionally, we found that MDMA increased social interaction and ratings of the attractiveness of another person in the room. Overall, these findings further highlight the potential influence of social factors in acute drug effects and may partially explain why MDMA is used in a social context. Future studies may examine the influence of a range of more naturalistic social settings and the extent to which socially facilitated alterations in subjective states influence MDMA consumption.