From these links, main number seems to be "Nearly 10 million Americans, or 4.1 percent of the adult population, used prescription opioid painkillers for nonmedical reasons in 2012-2013". Numbers I've seen for marijuana were about 11.5% in a year, though that was for 2001.
So certainly higher usage for marijuana, but definitely not "many orders of magnitude"
So certainly higher usage for marijuana, but definitely not "many orders of magnitude"