Not sure if this is what the other poster was going for but increases in spending in one area often comes at the expense of another area. That can come in the f

Not sure if this is what the other poster was going for but increases in spending in one area often comes at the expense of another area. That can come in the form of the illegal drug industry losing revenue to the legal drug industry and the government getting a share, but it also can come in the form of other spending that would have taken place now not taking place as users of legalized drugs are spending their money on those products instead of spending on going out to eat as often, buying fewer video games, purchasing less alcohol, going on fewer trips, etc. Tax revenue from that spending that has been displaced into the legal drug industry should be subtracted out of the $15 billion if the point here is that legalization increased government revenue. Of course, that's going to be very difficult to calculate since those displacement activities are on the individual level.