It simply get absorbed in the gut (like food or all medicines), into the blood. There is a 'blood-brain barrier' that many things cannot cross, but far from all

It simply get absorbed in the gut (like food or all medicines), into the blood. There is a 'blood-brain barrier' that many things cannot cross, but far from all. Painkillers, caffine, LSD, and other psychoactive drugs all cross this barrier by definition. In terms of damage, there are many possible mechanisms once in the actual brain tissue. Quite often drugs would act on a receptor on a cell, which would change how the cell operates in some way, such as by inhibiting an ion channel. https://en.wikipedia.org/wiki/Neurotoxin https://en.wikipedia.org/wiki/Neurotoxin