An explanation for 2 could also be drugs getting stronger. Given how much more potent modern cannabis is than it was in the 20th century, people might be spendi

An explanation for 2 could also be drugs getting stronger. Given how much more potent modern cannabis is than it was in the 20th century, people might be spending the same amount relative to THC content--but there's much more THC in a gram of cannabis than there once was, so they have to buy much smaller amounts of cannabis for the same amount of THC.