Sounds like you've bought into the
appeal to nature fallacy.
Cocaine and heroin come from plants. MDMA is a "designer drug"
http://en.wikipedia.org/wiki/MDMA
Furthermore, there are lots of designed drugs used for medical purposes. Does you theory extend to medical drugs? Lots of people seem to think that "natural cures" are always better. Are you one of those?
Uhhh....What? first, X would fall under the category of "safer" drugs that I was referring to. Is it naturally-occurring? Nope. But then, I didn't think I would have to go into detail, describing every single little illegal controlled-substance in existence.
Second, I am talking about the controlled substances that are purely meant for mind-altering purposes. Not for medical purposes. I thought this was pretty well implied, due to the nature of this discussion. I never imagined I would have to explain to anyone that we are not talking about such things as Tylonol, Allegra, Percoset, or any other pharmaceutical healing products; prescription or over-the-counter.
Now, when speaking in terms of the OP, not in terms of "medicine," generally speaking, most of the naturally-occurring substances are far better (less dangerous) than most of the designed **** that is on the black market right now.
And to preempt you, of course some of these "mind-altering" drugs can be used for medical purposes. Marijuana, for instance, is great for cancer patients in reducing pain. But then, so is alcohol. But at least maryjane is a hell of a lot safer than alcohol.
ETA: The so-called "fallacy" that you accuse me of, hardly makes any sense whatsoever in the scope of what I did say. Are you trying to tell me that naturally-occurring drugs, purely used for mind-altering purposes, are not as "good" as designer drugs meant purely for mind-altering purposes? They may not be nearly as "good" in the eyes of the drug user. But that wasn't the basis of my argument. The basis of my argument is that naturally-occurring drugs tend to be far less dangerous than designer drugs.
In fact, because virtually none of these drugs seem to have any health benefits whatsoever, or whatever benefits they do have, seem to be outweighed by the negatives.....the logical conclusion is that of course the designer drugs (designed to be a hell of a lot more powerful than natural drugs) would also be a hell of a lot more dangerous. Very, very few designer drugs are created by proper chemists in proper labs, and they have not gone through the proper channels of testing. Would you seriously trust such designer drugs that have created by amateur chemists, under amateur conditions? Or would you rather think that marijuana plant growing in your backyard is far safer than the designer drug that was created by "someone" whom you've never been given a name, much less ever met?