MDMA exerts its primary effects in the brain by increasing the activity of neurons that use the chemicals serotonin, dopamine and norepinephrine to communicate with other neurons. Compared to methamphetamine, MDMA causes greater serotonin release and somewhat lesser dopamine release. The serotonin system plays an important role in regulating mood, aggression, sexual activity, sleep, and sensitivity to pain. The excess release of serotonin by MDMA likely causes the mood elevating effects experienced by MDMA users. However, by releasing large amounts of serotonin, MDMA causes the brain to become significantly depleted of this important neurotransmitter, contributing to the negative behavioral aftereffects that users often experience for several days after taking MDMA.
Research in animals links MDMA exposure to long-term damage to neurons that are involved in mood, thinking, and judgment. A study in nonhuman primates showed that exposure to MDMA for only 4 days caused damage to serotonin nerve terminals that was evident 6 to 7 years later. While similar neurotoxicity has not been definitively shown in humans, the wealth of animal research indicating MDMA's damaging properties suggests that MDMA is not a safe drug for human consumption.
Further, MDMA can interfere with the body's ability to control its temperature, which has on rare occasions led to severe medical consequences, including death. Also, MDMA causes the release of another neurotransmitter, norepinehrine, which is likely what causes the increase in heart rate and blood pressure that often accompanies MDMA use.
It is also important to keep in mind that many users of Ecstasy may unknowingly be taking other drugs that are sold as Ecstasy, and/or they may intentionally use other drugs, such as marijuana, which could contribute to these behavioral effects.