The research on the pharmacology and toxicology of mephedrone is more limited than other commonly used drugs. This is because it wasn’t studied in detail until its use jumped from around 2009. We know more about other cathinones (extracted from the khat plant) which act in a similar way to amphetamines, acting mainly on noradrenaline and dopamine systems. It is thought that mephedrone also acts on serotonin. This is what may be the reason for its similarity to MDMA.
Cathinones (including mephedrone) act by inhibiting the reuptake of various transporters, very similar to the action of MDMA. However, slight differences in its chemistry may be the reason why mephedrone cannot cross the blood brain barrier as easily which means it has a lower potency compared to MDMA.