Do you have any actual evidence of this? I would love to see it. I wouldn't be particularly shocked either way to find that drug use has increased faster in places that decriminalized or not, but it's an important starting point for discussions. Assuming everyone is being honest in their data-gathering as well as consistent in methods.
Sure. For one, prohibition keeps the equilibrium price higher, which reduces equilibrium consumption. This RAND report from 2000 estimated a free market cocaine price would be 3% of the price under prohibition.
2nd, if you prefer a more direct account, this doctor describes the effects of BC's safe supply program. Basically they bought opiods and gave them out for free to addicts. These were often resold, crashing the market price, increasing consumption of these as a gateway drug. This is to illustate the expected effects of a lower price: https://www.theglobeandmail.com/opinion/article-we-must-end-...
Overall legal production is generally cheaper, and a cheaper price produces higher equilibrium use. You could of course tax legal drugs, but you'd need a war on illegal supply to enforce that.
