Can you tell me how drugs like mephedrone and cocaine damage the brain?

Nobody truly knows: what the toxic substances are and how they work, and also why some people use the exact same drug in the exact same amount and don't have adverse effects, while other people will have seizures on even lower doses. Stimulants put the brain in overdrive, and a particular part of the chemical of some stimulants (the methoxy- radical) seems to cause more damage. This is what is in bath salts and meth.