A study conducted by researcher Luke Downey of Swinburne University of Technology in 2015 sought to uncover the information behind MDMA-related health effects by looking at the levels of cortisol in the hair of heavy, light and non-users. Cortisol is a stress hormone released naturally by the body into our hair, and can be studied to find the level of stress we’ve felt in the past.
“Hair grows one centimetre per month. We took three centimetres of hair from the scalp of non-ecstasy users (control group), light ecstasy users and heavy ecstasy users to assess the level of stress on their bodies over a three month period.”
33 females and 28 males took part in the survey, with the average age of the participants being 24. After recording levels of cortisol over the course of three months, Downey found that heavy and light users of MDMA experienced noticeably higher levels of stress than did the non-users. Stress in light users was more than 50% higher than the control group, while heavier users were found to have four times the level. 
While Downey did find lower levels of memory performance in those who had taken increased amounts of MDMA, he said that the correlation between the two was not distinct enough to imply causality.
“In measuring both stress levels and memory performance, what we wanted to know was – ‘does that repeated stress on your body relate to memory problems?’ Interestingly, no significant relationship between the memory deficits and levels of stress (indexed by the amount of cortisol) emerged. This increased experience of stress appears not to be the mechanism that produces the memory deficit.”
Source: AJP
