Over the past three decades, millions of dollars have been spent on thousands of studies attempting to better understand the neurotoxic effects of MDMA. All of the clinical studies have recruited people who use ecstasy—a drug that does often but not always contain MDMA. Although most researchers agree that MDMA is the cause of neurocognitive deficits in ecstasy users, this consensus is based on a large body of literature with many limitations.
Amoroso, T. (2016). Ecstasy research: will increasing observational data aid our understanding of MDMA?. The Lancet Psychiatry, 3(12), 1101-1102. 10.1016/S2215-0366(16)30345-5