That would be an interesting study, but it's not relevant to the discussion of the war on drugs. The comparison you'd need to make it how those people you know would be doing if they were in prison for using illegal drugs. I'd wager they'd be doing worse.

I agree about that study being more relevant to the war on drugs, but my point was simply in response to the anecdotal claim about the motivation and success of drug users. If it were possible, it may provide more insight into how drugs should be viewed in society, regardless of legality.

In addition to baddox's comment, your comment seems to suggest that extremely productive/intelligent people have a duty to society which extends into their private leisure time. I find that burden to be absurd.

If they were enjoying a light marijuana buzz (or a light alcohol/caffeine buzz!!!) during work hours -- or in a way that directly and visibly effects their work performance -- you might have a point.

But even in those cases, I would still strongly disagree with your rationale. The same line of reasoning also justifies jailing people for obesity, which "Has Been Known To Significantly Decrease Productivity". And it certainly justifies jailing people who drink alcohol, since even mild hang-overs have rather extreme effects on productivity. If you're too over-weight or hung-over or high to work, then you should be fired. Not jailed.

But justifying a law on the basis that individuals should organize their private life choices such that they are optimally productive as members of society? That's quite the burden, and if we're going to impose that burden, I suspect we'd have a compelling justification for jailing literally anyone.