G Jones summarizes some new research on the effects of mephedrone.
The research done here indicates that there is no neurotoxicity caused by mephedrone to the dopamine systems in the brain. Amongst other things, these systems affect reward, learning, motivation, sexual gratification and attention span, and the fact that even in doses resembling significant binges (1-3g for a 70kg person) there is no damage here is very reassuring. That said, there is evidence which shows that mephedrone causes significant and persistent serotonin deficits, similar to MDMA.
Read the papers exploring mephedrone's effect on serotonin and dopamine. If you are a current student, it is likely you can read the papers by logging in through your university's VPN client or through Athens, or alternatively check it out at the library.