This is a randomized, blinded, placebo-controlled Phase 1 study that aims to evaluate the impact of 3,4-methylenedioxymethamphetamine (MDMA) on startle response . MDMA is an experimental drug and is illegal to possess outside of research; when sold illegally it is referred to as Ecstasy or Molly (material supposedly containing MDMA). MDMA may make it easier to face unpleasant memories and reduce anxiety.