Quote Originally Posted by mellow mood
lets what i would say to her: 50% of the world population smoke marijuana, 0,01% take heroin.
Not even close. According to various sources, the number of Americans who regularly smoke marijuana varies between about 15 and 20 million, mostly depending on the definition of "regular user". Given that the current US population is about 270 million, this works out to between 5.5 to 7.4 percent of the total population who are regular users. Obtaining worldwide figures is more problematic, but I can see no reason why we cannot extrapolate the US figure to a good first-order approximation. I don't know what the percentage of regular heroin users is, but no doubt you are correct that it is considerably lower than the figure for marijuana use.