Legalise marijuana and ban smoking anything.
By all means, eat it in brownies or cakes or make tea or soup with it, but please just don't smoke anything at all ever.
See how it worked out for Portugal? I can't really argue with that. Alright, the sample size is only one ... nation ... but still, it's a hundred-percent success rate so far!
I think to really answer this issue we'd need to build (using rods of wall building from Angband) a group of islands somewhere like the Atlantic, just east of the rift and level with Andorra, and cover them in compost and grow lots of trees with the help of a few hundred druids ... and then build a modern utopia there with two houses of parliament, one of elected constituency representatives and one proportionally representative of the population, and really good public transport and sustainable power generation ... and outlaw fishing completely in a large part of this new nation's territorial water and fucking well SINK the Japs' fleet when they come and try to kill whales there ... and make sure we make some of the islands tall enough to be year-round ski resorts because we'd be raking it in then ... and have some of them as nature reserves with no permanent human population at all ... and then use some of the islands as test groups in a huge experiment over four generations, because doing it with rats wouldn't necessarily give data applicable to humans.
Considering that the LD50 (oral) for rats translates to about a kilogram of 10% THC cannabis buds for an adult human and the LD50 seems to go up with increasing size, I think we can stay well below the human LD50 for this.
Doses of 0, 8, 16, 32, 64, 128 and 256 mg/kg,
administered every 3, 6, 12, 24, 48, 96 or 192 hours,
during ... er ...
Assign:
infancy 1
adolescence 2
young adulthood 4
pregnancy 8
0001 - during infancy only
0010 - during adolescence only
0011 - during infancy and adolescence
...
1111 - throughout life
... making 15 groups by life stage, 7 by frequency and 7 by dose for a total of 735 groups of rats ...
... and assess their ability to handle things like Simple Simon, mazes, clockwork puzzles and so on.
735 islands ... that's going to take some building.