(I'm not saying it is safe, but...) It's worth noting that all studies on the long-term effects of illegal drugs have to be done (by necessity) on people who generally, due to their lifestyle, are exposed to a myriad of products that are (potentially) harmful to their bodies, and for hardcore users, have other aspects of their lifestyle that expose them to risks (plainly put, drug users often use different kinds, drink, party and smoke a lot, and addicts are prone to being homeless and/or in prostitution, exposing them to various medical dangers). So it's very hard to isolate what effects are to be ascribed to the MDMA (or variants) and what to other factors.
