MDMA (3,4-methylenedioxymethamphetamine) is a Class A substance that is usually found in a tableted form. It is only observed in one orthorhombic polymorph under ambient conditions. It shows slight positional disorder around the methlyenedioxy ring which persists during compression up to 6.66 GPa. The crystal quality deteriorates above 6.66 GPa where the hydrostatic limit of the pressure-transmitting medium is exceeded. The structure undergoes anisotropic compression with the a-axis compressing the greatest (12% cf. 4 and 10% for the b- and c-axes, respectively). This is due to the pattern of the hydrogen bonding which acts like a spring and allows the compression along this direction.