[sibeliuss]

All of the other responses are accurate -- combining the two will augment and possibly lengthen the experience -- but if you're familiar with both substances enough to feel confident in combining them, I've always found that 70mg dose of MDMA and a big glass of water will pull me right out of a trip that's heading south, and pretty quickly, into more glorious places.

But again, disclaimer: this is really only for folks experienced enough to know how to navigate each separate space well, and for those that have confirmed, tested, pure, high quality MDMA.