Like how the Wild Lettuce herb once was used as a kind of methadon. Until the 19th century 'Lactura' was used as a method to get rid of an opium addiction. Heroin is a result from the ban on opium. Cocaine is more easy to smuggle than the healthy coca leaves which, by the way, are still used in the Coca Cola formula. The Coca Cola company is the only legal entity that is allowed, by international law, to import coca leaves from South America.
Strange thing is that nobody knows what happens with the cocaine produced.
Nothing so unlogical as narcotic policy. That's of course also the nice thing. Till the catholic church came to forbid the usage. The Vatican also forbid the use of coca leaves in colonized South America. Although this decision was redrawn when the imperialist countries found out the Indians where more efficient in the Gold mines with the coca leaves.