Illegal to manufacture just means the people who can legally possess it will have to deal with and buy it from people illegally manufacturing it under poor conditions with zero regulatory accountability.

And some of them will get sick or die because of the prohibition on regulated manufacturing.

We know that because there isn't an epidemic of people going blind and dying after drinking alcohol contaminated with fermentation and distillation byproducts, but there is an epidemic of people dying from using "heroin" tainted by fentanyl analogs.

The only thing that has ever worked is legal regulated sale, which keeps the market sane with respect to quality control and safety, while making it easy for people to access health and addiction services.