Weed is not a gateway drug, I've heard over and over. You must have that story confused somehow.
Long story short...couldnt find ANY statistics on this but whilst working on a thesis I needed to know the incidence of marijuana being found in the company ( same venue or vehicle) as the hard narcotics.
Had to poll all the cops I know-which was a bunch- in five different states. The consensus was well over 60% of the time when hard drugs were found, marijuana was present.
Coincidence? I think not.
Make of it what you will.