They restrict the damage that is caused by this kind of drug, in a similar way to the way they have restricted the damage caused by addictive drugs in the present, and the past.
One dangerous side effect of 'stay alert' or 'thought accelerators' is that often they can be taken at the expense of the minimum required amount of sleep (which can vary from person to person.) Sleep is necessary for our brains to operate properly, and they've yet been able to find any cases where it can be compromised to any great extent. Sleep deprivation can lead to delusion and psychosis, poor concentration, and performance, and both short and long term memory loss. A bad combination. Where too many 'flashes of brilliance' are really just flashes.
By the way. Who is going to test these drugs. Perhaps we'll have some smart monkeys that will unify Einstein's 'Grand Universal Theory' for us. I'm sure they'd find it much easier to be objective. (Douglas Adams told us what happens when you have smart mice