As shown in the report I linked before. Meth is a highly regulated hard drug that can be obtained legally. [1] Mexican drug cartels still traffic it, still makes tons of profit from it, thousands of people die because of it. Regulating Meth didn't stop the drug war.
What exactly makes you think any other drug would be different?
When most people refer to the legalization of "drugs", they are typically implying decriminalized (or semi-decriminalized) recreational use and not tightly regulated medical use (Desoxyn).
This makes sense, since a highly regulated substance is de-facto illegal if it is unobtainable by the vast majority of its target market.
Excuse me, but it's NOT legal. It's not legal to produce and it's not legal to sell or buy. Therefore, it's not being produced or sold by legitimate operations. THAT is why Mexican drug cartels still traffic it. Because it's still illegal.
Desoxyn is pharmaceutical methamphetamine. It is extremely infrequently prescribed, but technically more legal (schedule II, along with cocaine) than LSD or Marijuana (schedule I).
What exactly makes you think any other drug would be different?
[1] http://en.wikipedia.org/wiki/Methamphetamine