A new study of MDMA self-administration in monkeys found MDMA to be far less toxic than assumed from previous studies. Study findings suggest that when monkeys take doses of MDMA similar to those used by Ecstasy-using humans, there are no signs of harm to serotonin or dopamine cells. Study findings also suggest that monkeys, like humans, may slowly lose interest in taking MDMA over time, and that this change of heart is not a sign of brain toxicity.