A recent study published in the International Journal of Drug Policy estimates that 50 to 80 percent of inmates in Swiss prisons use marijuana. Prison staff told researchers they found marijuana to be a relatively safe drug and that cracking down on consumption would have more negative effects than positive ones.

Surveys of detainees and guards revealed similar opinions on marijuana use, with both groups describing the effects of marijuana as analgesic, calming and a way to decrease the traumatic prison experience. Negative consequences included sleepiness, social isolation, and decreased perception of danger. But survey participants also said that more restrictive regulation could increase fear, trafficking, and a shift to harder drug use. 

While prisoners estimated that up to 80 percent of prisoners use marijuana, guards reported a lower estimate at 50 percent. Read more about it here.