I'd go with Eddie's version.

Remember, all drugs were legal until relatively recently. Then there was a review of the relative dangers of each drug. Some, like pot, were deemed to be dangerous to health and to have no medical benefits, and so were criminalised. Others, like heroin, were deemed to be dangerous to health but to have medical benefits, so you can be prescribed it as a painkiller.

Trouble is, there's been no update on these rules for the last 40 years or so. All the recent medical evidence on pot has been ignored. I find this bizarre. OK, maybe you don't want to make more drugs available for distribution like alcohol and cigarettes - I have no real problem with that, although I don't think it's really justifiable. But when a chemical has been shown to have medical benefits and mere political issues stop it being available to treat people, that's crap. You can be pumped full of heroin as a painkiller, but you're not allowed to take pot to minimise the effects of chemo? Bizarre.

Graham.