Well, it's not surprising that drugs can help with cognition. But we've to be very careful about two things : the effects it has on other parts of the body, and the long-term effects, both to the body and to the brain itself.

The human body is a very complex and delicate machinery, and the human brain the most delicate part of it... it's very easy to create long term problems in it by trying to push it a bit too much. Just look at the professional sport players, and how badly they are damaged after a few years of taking drugs to enhance their performances.

That's why I tend to be very careful about not taking drugs, unless I already have a disorder that needs fixing, and unless advised to take them by a doctor I trust. Taking drugs to increase performances sounds a bit like overclocking CPUs. Sure they'll go faster... but at the risk of increasing bugs, and of a shorter lifespan due to increased heating.

Now if a drug is really efficient, with no side-effect, no long-term consequences, according to very strict peer-reviewed studies, then ok. But until then, my motto is "careful, your body is complex and delicate, we don't fully understand it, so unless you really have a problem, don't take drugs".