All stimulant drugs (like cocaine, amphetamine and mephedrone) work in much the same way. They all cause the release of chemical transmitters such as dopamine and serotonin. As they draw from the same source, using more than one will lead to more rapid exhaustion. Combined use also seems to lead to an increased risk of unwanted stimulant effects such as palpitations, panic and aggression. Oddly enough, many users say cocaine reduces the buzz from MDMA—which is probably why most users avoid cocaine with MDMA.