Actually, making drugs illegal is the wrong way to solve the original problem, and it creates numerous others. You have people getting guns to shoot the cops when they are busted, it makes the prices (and profits) higher, and people are more likely to rob and steal to get their drugs. In the free market, drug prices would be driven down so there would be no huge profits, no pushers, and fewer new addicts (and less robbery and burglary to support it).
The best way is to ask why people use drugs in the first place. It is because our education system is sxxx, and fails to stimulate people. (Notably, the biggest drug problem is not on the streets, but in the doctor's office--we have a bigger Ritalin problem than a weed problem). It is because people are not allowed outside the box that the regulators create, and that fails to stimulate. Stagnation results in people needing to escape, and drugs (and other kick crimes) are the escape that many choose.
All they would have needed was to eliminate the choking regulations. Children who are properly stimulated to learn in school almost never play hooky, even if they could get away with it (and are rarely "sick", rarely to never cause disruption in school, and just about never use drugs or drink). And they actually learn in a more integrated way, allowing breakthroughs that we do not have today (and they are not limited to "in the box" or mainstream solutions to common problems). Such people will get more kicks out of learning than they ever could out of drugs, so drugs cannot compete.
At which point, the demand for drugs would implode. Fewer people wanting drugs means fewer drugs being sold. There will be a backlog of unwanted drugs that they can't even give away, and ultimately more weed, cocaine, heroin, and other drugs would simply be thrown away than ever get raided in all the drug busts in the world. Producers would lose money, and would quit wasting time producing them. All without a single arrest, a single fine, or a single raid--the drug market would just die on the vine.
Or, we could continue wasting time and money raiding people only to have profits go even higher. And that would drive up the supply, inciting more drug pushing and more wasted time and bullets (and good neighborhoods). Heck, they might as well criminalize any substance that might make one feel good--including harmless substances like magnesium, vitamin B12, folic acid, and vitamin C. And create more problems of enforcement and secondary crime in the process.
