People who use MDMA can become dehydrated through vigorous activity in a hot environment. It may not seem like a big deal, but when MDMA interferes with the body's ability to regulate its temperature, it can cause dangerous overheating, called hyperthermia. This, in turn, can lead to serious heart and kidney problems—or, rarely, death. MDMA can be extremely dangerous in high doses or when multiple small doses are taken within a short time period to maintain the high. High levels of the drug in the blood stream can increase the risk of seizures and affect the heart's ability to maintain its normal rhythms.