Scientific sources for MDMA 1-3 month rule

The 1-3 month rule is an estimation based off the aggregate of the data that we have. It's going to vary from person to person, and from situation to situation. A young person that eats well, keeps their dosages reasonable, and keeps their body temperature down, is going to be able to have shorter intervals between use than someone who has a poor diet, uses high doses, and dances all night till they are overheated. As Borax said, we cannot design a study that can prove this rule ethically, as it would be subjecting one group to known neurotoxicity. But the proof is in the pudding, so to speak. Take MDMA every week for a year, then run some standardized cognitive assessment tests. I guarantee you'll see statistically significant decreases.

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If you want scientific proof that MDMA can be neurotoxic in humans, here are some sources:

Here's one that found a reduction in SERT in former ecstasy users

Here's another one that had similar results

Here's one that noted "long-lasting changes in brain function consistent with 5-HT toxicity"

Here's one that found decreased serotonin binding in users

Here's one that found long-term effects effects on central neuronal activity in humans

Here's one that found a long-lasting increase in cortical excitability in former users

Here's one that found reduced cortical SERT binding in former users after months of abstinence

Here's one that found NO improvement in verbal memory in former users 2.5 years of abstinence

Here's one that found long lasting serotonin system impairment in former users

Evidence from human studies has accumulated more slowly, but it is becoming apparent that the toxic effect of MDMA on central serotonergic systems found previously in animal studies has a clear parallel in human users of the drug.There is now direct evidence of a lasting decrease in 5-HT uptake sites (a marker for the integrity of 5-HT nerve terminals) in human volunteers with a past history of MDMA abuse

Here's the source

This meta-study found CLEAR evidence of neurocognitive decline in former MDMA users and clearly states there is DIRECT evidence for neurotoxicity.

Here's one from Hong Kong that found abstinent users were impaired in memory, verbal fluency, and complex attention

Here's another that found memory impairments and the researchers believe it is directly caused by Serotonergic neurotoxicty

Here's one that found memory impairments in abstinent users and evidence of PFC dysfunction

Here's one that found a direct relationship between amount of usage and amount of declarative memory deficit

Here's one that found that heavy users had a weaker blood oxygenation level-dependent response during a working memory task

Here's one that found hippocampal damage in chronic users

Here's one that found diminished hippocampal activation during memory retrieval

Here's one that found toxic effects on the thalamus

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Yes, these studies cannot completely control for poly-drug use during that time period. However, when clear patterns start to arise that mirror findings in animal studies, it's hard to overlook the evidence. Given the evidence that we have, it's reasonable to assume that longer periods between use are going to lead to less damage and less down-regulation of 5-HT receptors and enzyme expression. When looking at all the data, 1-3 months is the time I would recommend between uses, for the average user. Does that mean that taking it more often than that is definitely leading to irreparable serotonin system damage? No, it does not. However, given the knowledge we have, a reasonable person would make the choice to at least wait 1-3 months between MDMA uses.