That is perhaps a fact, just as having no government does not ensure your freedom, is a fact. I say perhaps may be a fact, because it may add freedom to some while taking from others. So it really depends upon your point of reference. If it held true for all, then no one would be for it and government would have to resort to force to increase power. Believe me, I am for a much smaller government at all levels, but especially at the Federal level
However, I asked what your solution to the problem is. You seem to think the problem is only the WOD, which in reality was just the ineffective solution created to solve the ills drug usage inevitably create. While drugs affect the users, they sadly are not the only ones affected. It affects those who come into contact with them on a regular basis, wives, husbands, and their offspring. Furthermore it has an adverse affect on society at a whole. With increased costs for healthcare, property losses & damages, and increased violent crimes against persons ranging from battery, rape, to even murder.
There is no evidence suggesting government can solve the problem of drug abuse - but plenty of evidence that it can make things worse.
While drugs affect the users, they sadly are not the only ones affected.
Almost everything anyone does "affects" someone else; if that's the test for government authority, we can kiss freedom goodbye.