I order to give you a REAL answer, the mechanics of the underground ecstasy marketing conditions must be examined;
Most people pressing the pills didn't make them, to put it simply, and the person pressing the pills HAS THE FINAL SAY about whats actually in them. Pure MDMA
cannot be pressed, it simply won't hold together.
BUT...sometimes the chemist IS pressing the pills, and meth still ends up in there.....why?
Money.
Pure MDMA, the real thing, isn't as speedy as people think...many people have not CONSISTENTLY done real MDMA over a period of time, or this would be common knowledge.
It used to amaze me when people would ask me, 'Man, what DID you give me'?
me: the real thing....what a trip, huh?
But I'm going to tell you whats REALLY A TRIP....most people who use it casually would rather have speed in there.....people,genrerally are stupid in this area, is what I have concluded. I know it sounds a bit harsh, but its true.
You'll notice I said 'people who use it casually'.....because these people are superficial, usually, trying to get fucked up, and the magic of real MDMA is WASTED on them.....THIS IS WHY so many pills are adulterated with all kinds of shit, from caffeine to meth and everything in between.
People tend to not have very good understanding of MDMA, and I can somewhat understand this, but Jesus, if you didn't want to experience what it has to offer, why'd you go looking for it?
It used to STUPIFY ME to watch people start drinking alcohol while rolling, or snorting meth INTENTIONALY...these dimwits had no business being in the same room with me...and mdma tends to work as a truth serum of sorts with me, and I would frequently speak my mind on this subject.
People are generally not on that high of a level, mentally, concerning this subject, which is why there is so much exploitation and bullshit involved.
I NEVER,EVER cut my stuff.......but everyone who got hold of it did, usually with speed.
I woke up......the truth is, and I will sound like a dickhead saying this;
Most people aren't worthy of MDMA because they don't want what it has to offer.
As to how they interact:
The meth overpowers the mdma, to be direct.......shifting the effects toward the physical end of the spectrum, enhancing the stimulant effedts, and depressing the other, more subtle, more valuable effects.
Pills with speed cut in them develop a rep as 'more potent' or 'speedier', and the meth does interact with the mdma and may even make certain aspects of mdma more intense.....I think meth sucks, I hate it, and I'd laugh in someones face if they suggested that I take it in that context.
So, the answeer is the usual suspects.....greed and ignorance.