For the most recent issue of National Review, I interviewed Dr. Robin Murray, one of Britain’s leading psychiatrists, whose work on cannabis-induced psychosis is worth serious consideration. Murray explains:

If 100 people smoke cannabis with 15 percent THC content every day, five of them will develop frank [i.e., blatant] clinical psychosis; if they smoke cannabis containing 30 percent THC every day, then 10 of them will develop psychosis. This compares with 1 percent risk in the general population. For comparison — in 100 tobacco smokers, about 10 will get lung cancer.