They might not even notice. Didn't Aldous Huxley warn us of this kind of thing? People are under the illusion this drug is not addictive. If that's true, how come people seem to smoke it really rather regularly when they're into the habit?
In the Brave New World, all manner of chemical escapism, feel-good stuff and drug-taking is encouraged because it keeps the masses happy, or at least passive enough not to realise the nature of the prison being erected around them.
It is at least worthy of discussion why, at this point in history, powerful leaders want the people to get stoned and be sedated, lacking in motivation and high. Smoke the arguments for legalisation by all means, but don't inhale. It does alter your mind and not for the better.
I'm sure that, as well as studies linking cannabis to schizophrenia, depression, inertia (see, I don't need pot) and lack of motivation there must be at least one Catholic study linking the smoking of pot to a sudden decline in Mass attendance, abandonment of the praying of the Rosary and of a decline in the frequenting of the Sacrament of Confession. Oh, and perhaps a more laissez-faire attitude towards sin in general. I believe it was the drug that inspired a whole generation forty odd years ago to 'chill', 'lose their inhibitions' and 'go with the flow'.
From what I know from people who have been in prison, I know that a certain amount of certain drugs are allowed inside the prison walls. It stops them from rioting, you see and makes the prison population more 'manageable'.