MDMA does not build tolerance exponentially -- in any reasonable use of "exponentially"
going from power 1 to power 2 would be going from 100 mg to 10 grams
It actually quickly builds complete tolerance (detailed by shulgin below)
NOTE -- very high doses of MDMA result in large amounts of metabolites that are ACTIVE amphetamines -- there is no data on the tolerance profile of these metabolites. There is likely some, however, the metabolites are likely the cause for the increasingly speedy, cranked-out feelings associated with post tolerance high dose bingeing reported by some users.
Furthermore the tolerance disappears as quickly as it comes
" Tolerance studies also support differences in mechanisms of action. In one study, MDMA was consumed at 9:00 AM each day for almost a week (120 milligrams the first day and 160 milligrams each subsequent day) and by the fifth day there were no effects from the drug except for some mydriasis. And even this appeared to be lost on the sixth day. At this point of total tolerance, there was consumed (on day #7, at 9:00 AM) 120 milligrams of MDA and the response to it was substantially normal with proper chronology, teeth clench, and at most only a slight decrease in mental change. A complete holiday from any drug for another 6 days led to the reversal of this tolerance, in that 120 milligrams of MDMA had substantially the full expected effects. The fact that MDMA and MDA are not cross-tolerant strengthens the argument that they act in different ways, and at different sites in the brain. " - Alexander Shulgin, PIHKAL #109