When considering the risks of "recreational" chemicals, it helps if we distinguish between moreish and addictive. By moreish I mean the tendency to lead to compulsive redosing, and of course when I say addictive I mean in the medium to long term. These can be surprisingly independent. In the case of MDMA, the consensus among drug users, in my experience, is that it's medium high on the moreishness scale but very low on the long term addictiveness scale. In my opinion there is pretty much 0 danger of addiction for the vast majority of less wrongers.
However, from personal experience it can be a very dangerous social lubricant, it lead to multiple social interactions that I later regretted strongly, and this seems to be pretty common.
Thus spake Eliezer:
It seems that many here might have outlandish ideas for ways of improving our lives. For instance, a recent post advocated installing really bright lights as a way to boost alertness and productivity. We should not adopt such hacks into our dogma until we're pretty sure they work; however, one way of knowing whether a crazy idea works is to try implementing it, and you may have more ideas than you're planning to implement.
So: please post all such lifehack ideas! Even if you haven't tried them, even if they seem unlikely to work. Post them separately, unless some other way would be more appropriate. If you've tried some idea and it hasn't worked, it would be useful to post that too.