Here's a nice little graph, showing the carefully worked out levels of harm that are caused by various drugs. This was part of the report the British government funded, which resulted in them sacking the scientist in charge of the research, because he wouldn't say what they wanted him to say.
It's a little out of date, as the latest absurd Home secretary, Theresa May, has just decided that khat is now so dangerous it has to be made illegal. That will provide a nice little earner for the gangs that will spring up to make sure it can still be obtained just as easily, and who will get rich enough to become Tories, while probably harming competitors with guns. Way to go, Theresa!
In the meantime, the government does nothing to stop us drinking ourselves to death on Victory Gin, and smoking cigarettes. That, of course, has nothing to do with the huge taxes levied on alcohol and tobacco, nor the fact that their manufacturers donate huge sums of money to the Tory party.
The easiest way, incidentally, for any party out of the three very similar ones we suffer from to win a majority in an election would be to announce the legalisation of cannabis, and proper programmes to mitigate the harm of the others. They are unfortunately all too stupid to give that a go.