Ricaurte and McCann point out, these differences are generally considered positive. Furthermore, these findings are perplexing in that the generally held view is that lower serotonin levels lead to more hostile and impulsive behavior, not less. As with most MDMA neurotoxicity studies so far, this one raises more questions than it resolves.
More research is required to sort out the findings.
One difficulty in interpreting the results of this study is that comparing people to matched controls is as much art as science. People are wonderfully unique, especially so when it comes to serotonin. Finding a perfectly matched control is almost impossible since the normal level of brain neurotransmitters varies enormously between individuals. Nevertheless, comparing people who have used MDMA many times in the past to matched controls who have not used MDMA does have some advantages over a controlled study administering only a few doses of MDMA to its subjects. Data from both sorts of studies, with matched controls or subjects as their own control, will be needed to assess more fully MDMA's complex and fascinating effects.