If you try to tax drugs, there will still be a significant black market. Just look at cigarettes - legal, but huge black market because there is money to be made undercutting legitimate vendors with taxed goods.
But then again, there is a somewhat thriving black market for detergent and soaps: In the US, Tide is often targeted, as are branded department store body soaps, shampoos, and razor blades. This isn't because soaps and things are taxed.
Also, does tax make up for all of the risk markup? I very highly doubt it. IIRC, prices have gone down in places with legalization, in no small part because the whole process can be done out in the open.
In New York there's a $4.35 excise tax on a single pack of cigarettes. In Missouri it's $0.17. That huge delta provides a big opportunity for arbitrage.
And there are lots of people involved, each one adds markup.
The cigarette tax rate in New York is 2500% higher than the tax rate in Missouri. That's more than a few %, and that's just the state tax; NYC has their own additional tax that increases the difference even more.
A black market only exists when there's legal hurdles to avoid. Some markets have low enough legal hurdles, that there's no black market.
(But I agree with the rest of your comment.)
Eg some countries have black markets in currency, because of tight controls. Singapore doesn't really have black markets in currency, despite some (light!) regulation and taxes on money changers.