The most important reason for the increase in opiate consumption in the United States during the 19th century was the prescribing and dispensing of legal opiates by physicians and pharmacists to women with "female problems" (mostly to relieve menstrual pain). Between 150,000 and 200,000 opiate addicts lived in the United States in the late 19th century and between two-thirds and three-quarters of these addicts were women.[35]

Prior to 1890, laws concerning opiates were strictly imposed on a local city or state-by-state basis. One of the first was in San Francisco in 1875 where it became illegal to smoke opium only in opium dens. It did not ban the sale, import or use otherwise. In the next 25 years different states enacted opium laws ranging from outlawing opium dens altogether to making possession of opium, morphine and heroin without a physician's prescription illegal.

The first Congressional Act took place in 1890 that levied taxes on morphine and opium. From that time on the Federal Government has had a series of laws and acts directly aimed at opiate use, abuse and control.

The thing that always baffles me is it's not actually illegal to have drugs in your bloodstream nor is it illegal to consume them.  Which makes no sense, you can't own them, sell them, or buy them.  But being under the influence is fine, or at least not illegal.

The only point in the drug stream in which they are legal is when they are actually effecting your mind.

So actual usage is not illegal in a war whose entire goal is controlling usage.  Makes no sense and proves that even the anti-drug zealots realize what we put in our bodies is pretty damn sacred and not to be F'ed with.  So they go after the other portions of the stream, possession, buying, selling, and of course transporting and manufacturing.  But they never F with being under the influence beyond things that could hurt other people like driving.

Though the fact we used to roll that way is evidence the sky won't fall if we do repeal prohibition.

There is absolutely no evidence of that.  We are a completely different society now - more people, more impatience, and in many ways, more violent.  The environmental factors alone that we deal with - no one has any idea how those combined with the drugs you are talking about will affect those taking it.  Plus, many of the drugs today have other ingredients and fillers that weren't there 100 years ago.  

And, there's many more opportunities for people to hurt themselves, or more importantly, hurt others.  Off the top of my head, I'm thinking about cars and machinery.