http://thebrain.mcgill.ca/flash/i/i_03/i_03_m/i_03_m_par/i_03_m_par_ecstasy.html
This is how MDMA works on our brains. It releases a large amount of serotonin, as shown in the diagram in that link. Most of our serotonin is found in our guts i believe. It is a Vital Neurochemical that effects our appetite/sleep patterns/quality of sleep/ energy levels/ concentration and general mood.
Lack of sleep / Anxiety / No appetite/ Depression / Low energy are some of the most common complaints that i read on here from using mdma too often.
The minimum wait between mdma use is 30 days. But it should be more around 60 - 90 days, however i know from seeing it firsthand that people especially in the uk just eat so much mdma.
If your using it weekly, it will seem weaker.
For example a friend of mine whos been raving for years, £20 worth of mdma lasts her a few hours.
£20 of mdma lasts me about 4 nights out minumum and hits me wayyyy harder.
Your tolerance will build (Which is basically just you are releasing too many neuorochemicals in your brain) you need to give them a chance to replenish.
Ive been using mdma for 12 months now. Ive used it about 13 times in that space of time.
Ive been using it nearly once a month, there was just once i did it 3 weeks later.
I have an amazing magical time on it, but ive noticed the last time, it wasnt as enjoyable, so im going to aim for once every 2 months.
Hope this helps