MDMA makes people more cooperative and trusting – but not idiotically so. At least, that's the conclusion of a study examining the effects the drug has on interpersonal behavior recently published in The Journal of Neuroscience.

MDMA – technically known as 3,4-methylenedioxymethamphetamine and informally as Molly – is the main ingredient in Ecstasy. Best known as a party drug, it releases dopamine, noradrenaline, and serotonin, the latter causing temporary feelings of euphoria and heightened sociability. Even, as it turns out, in cephalopods. 

But it's not really understood how or why it has such an effect on social processing and cooperative behavior. So to find out, researchers from King's College London (KCL) recruited 20 healthy men and had them play a game called the Prisoner's Dilemma while hooked up to an MRI scanner. 

The Prisoner's Dilemma is a two-player strategy game whereby each player has to decide whether to cooperate or compete with their opponent. If each player competes, both end the game with a low score whereas if they cooperate, both get decent points – making cooperation the mutually beneficial strategy. However, just to throw a spanner in the works, if player 1 chooses to compete and player 2 chooses to cooperate, player 1 nabs all the points while player 2 is left empty-handed. 

For the experiment, the volunteers – some of whom had been given 100 milligrams of MDMA and others a placebo – were made to think that they were playing against real people via a computer. In actual fact, they were playing against pre-programmed computer responses that had been designed to "perform" in a trustworthy or untrustworthy manner. 

While MDMA did appear to make the volunteers more forgiving and cooperative, this magnanimous behavior was only awarded to players they judged trustworthy, ie the players who took the cooperative strategy much more often than the competitive strategy. This, the researchers say, suggests that MDMA may make you more trusting but it does not make you particularly gullible.

"When trustworthy players betrayed the participants the breach in trust had an equally negative impact whether participants were under the influence of MDMA or not," first author Anthony Gabay, who carried out the research while at KCL but is now at Oxford University, said in a statement.

"However, MDMA led to a quicker recovery of cooperative behavior and this tendency to rebuild a relationship led to higher overall levels of cooperation with trustworthy partners." 

This result was backed up by the MRI scans, which showed increased activity in the superior temporal cortex and mid-cingulate cortex among the volunteers who had been given the MDMA dose. These two areas are related to our understanding of other people's thoughts, beliefs, and actions.

In particular, the researchers highlight changes to the right anterior insula, which is linked to all things associated with appraisals, risk, and uncertainty. This, they say, increased in the brains of volunteers who had taken MDMA when they were processing the actions of players deemed trustworthy but decreased when processing the actions of players thought to be untrustworthy. 

“Using MRI scans, we were also able to see that MDMA had an impact on brain activity when processing the behavior of others, rather than altering the decision-making process itself,” Gabay added.

So, what now? The researchers hope the research can help scientists identify "what goes wrong" in patients with psychiatric conditions and improve understanding of how MDMA can be used as a medical tool. Already, trials have looked into how the drug can be used to treat a range of conditions from PTSD and alcohol addiction to social anxiety in adults with autism spectrum disorder.