And you have to keep in mind with any sort of pharmaceutical there's a major bias in research. There's billions of dollars to be made by showing that things are effective and safe. There's much less of an incentive to to show that things are ineffective or unsafe. Even for those who are genuinely completely altruistically motivated, there's far more interesting research to pursue and topics that don't come with lovely consequences such as making influential enemies within the industry you're dependent upon grants for.
Consider things like cigarettes, leaded fuel, or whatever else. There's invariably decades of "science" proving it completely harmless before some crisis points triggers a 'reevaluation'. And for things intended to interact with your cognitive abilities, if there are negative effects it's entirely possible we might never reach that crisis point as any negatives effects may likely manifest in ways that are rather less apparent than the effects of e.g. lead or tobacco consumption.
A general question I've been wondering about -- ever since it seemed half of some CS departments' undergrads were on meds, at the start of the dotcom bubble -- is what are the costs to discretionary use of meds as performance enhancers, by people who don't have abnormal brain situations to start with?
I'd like to know in general, and it might be important to public health or societal direction. But this doesn't seem the kind of thing that a non-researcher/doctor can ask individuals about, since it can be extremely personal.