A reader writes:

My wife was a pharmacology research focusing on marijuana many years ago, and ultimately left the field because the restrictions on marijuana research were just too onerous. The situation hasn't changed much in the intervening decades. You're only allowed to use marijuana grown by the government at the one place where they do this; it's not comparable at all to what's available on the street. Grants would sit forever at the NIH; and stop dreaming about clinical studies.

When the official government position is that this is a Schedule 1 drug, you're never going to find the funding for a large-scale double-blind test. There are plenty of studies, but not of the size and quality that should be available. I find The Economist's position to be most sensible: Legalization is the least bad option. Legalize it, tax it, and provide help for abusers on the scale of what we provide for alcohol or cigarettes. Yes, there'll be people who are hurt by this, and lives ruined; but all the evidence so far indicates that these will be far less than the damage to society from Prohibition.