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.
https://www.rand.org/pubs/reprints/RP909.html
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-...
This widely cited study on prohibition of alcohol in the USA found a long run 30% cut while prohibition was in force, with a sharper initial cut: https://www.nber.org/system/files/working_papers/w3675/w3675...
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.