On the very safe side: Not more often than every 6 weeks. Ideally not more than 15 doses in lifetime (that's what MAPS guidelines say). Stop once you are sad beyond the 'blue Tuesday' (not everyone has a blue Tuesday, but after repeated use it usually starts to happen and gets worse). There is quite some literature, sadly not nicely structured and concentrated in one place as far as I know.

I belive what you're saying isn't true and neither can I find a direct link to a MAPS guideline saying anything about the 15 doses in a lifetime.

In my experience I had blue mondays way worse on my first 3 times, and then I've got to the point where I am no longer blue on the days after. That would be my 6 times over a 5 year period.

I would have to search for that, but limiting your total cumulative dose makes sense in light of research showing adverse brain changes in longtime and/or heavy users.

The 6 weeks number is more a rule of thumb. For some it's longer, for others shorter. In the beginning, it may not matter, but if you browse drug forums for a while, you'll see the pattern 'don't do it too often' emerge.

6 times over a 5 year period looks quite safe. I have some friends who have used MDMA more than that and some of them started to have longer 'sad' or 'depressed' periods, sometimes stretching into months. Again, it would be great if there was an authoritative manual for all of this, but I don't think something like that exists.

Probably best to get a testing kit from e.g. DanceSafe[0] to at least confirm the stuff you've bought has MDMA in it. It is not uncommon for meth or other stuff (2C-B, or just inert filler) to be sold as MDMA.

(For the pedants: the positive test for the presence of MDMA does not prove that the substance isn't adulterated, but it's certainly better than a negative result.)

[0]: https://dancesafe.org/

Read Phikal by Alexander Shulgin, plenty of interesting information in there.

Really? I'd always thought Shulgin's PiHKAL [0] (Phenethylamines I Have Known And Loved) was more of a technical book. I'd never realised there was a more qualitative aspect to it. I'll be sure to check it out!

[0] https://en.wikipedia.org/wiki/PiHKAL

Yea the first half of the book is a brief story of his life, that's a really interesting read for sure.

Scott Alexander has an interesting review: http://slatestarcodex.com/2016/08/11/book-review-pihkal/