Is this true with regard to all drugs, and for all reasons? For example, could a physician decide to prescribe narcotics for anxiety? Or an athlete steroids to increase performance?

I will also ask again whether these drugs should be illegal. From my point of view, it seems logical that anybody should be able to use whatever drugs they want, so long as that drug use does not affect others. So, for example, heroin would remain illegal due to the strong negative externality imposed on a community by heroin users.

Mental performance enhancing drugs don't seem to have any negative externality associated with their use. In fact, the argument could be made that by furthering scientific discovery, they actually have a net positive effect.

I find no compelling evidence in favor of the prohibition of these drugs.