Idk about xtc, but i know you aren't supposed to take molly more than once every 3 weeks or so
some people took molly 3 days in a row and committed Self Delete because of the depression afterwards.
You'd have to take a forget load of molly over 3 days to have that severe depression. If anyone has any Ecstasy questions please refer them to me, I like to consider myself a bit of an expert on the subject.
The proper amount of time between doses is highly variable based on how much you actually dosed before hand. For a given person it'd take, maybe 500-700mg of pure MDMA (5ish good doses) over 2 or fewer days to deplete 100% of your brain's reserve serotonin, throwing you into wailing depression. That's kind of ridiculous, 5 doses equates to roughly 15 hours of rolling, over 2 days that'd be rolling for more time than you're in school for on each day. So you'd really only do that at a festival.
That's not to say if a good chunk of your brain's reserve serotonin is gone you won't be depressed, it just won't be nearly as bad. An average dose of MDMA is probably about 100mg (really depends on where you're getting it from, it could be 0mg or 250mg) so you wouldn't want to do more than 3 doses over 3 days (how you spread them is irrelevant, you can do 2, 0, 1 or 3, 0, 0) or you'd be feeling tuesday blues. After those 3 days though you'd want to give your brain some recovery time.
As far as general safety goes, it's pretty hard to OD on MDMA and it has a fairly fast metabolism rate so it won't build up over doses in your body. That's not to say it's impossible but it shouldn't be a worry. Drinking too much water is your biggest worry. Pretty much everyone that does MDMA nowadays knows to drink water to avoid dehydration, but if you drink too much you can get hyponatria and die. Don't do that. It's not easy to do either but don't go downing gallons of water in fear of dehydration.
Oh, also, take
this the next day. It's sold OTC and it's metabolized directly into serotonin so it will help with the depression if you happen to take a large dose.