I'd always consider that in situations like this "do not do anything harmful" is very different than "have not currently been proven to do anything harmful". In nearly all scenarios we're still very much in the latter case than the former. We're still discovering new negative consequences of things such as acetaminophen and aspirin which we've been consuming for, at least in the later case, literally thousands of years.

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.