The culture helps determine the setting of drug use, but so do the laws. Prohibitions enhance the dangers not just of drugs but of the settings in which they are used. The relationship between prohibition and dangerous adulterations is clear. So too is its impact on the potency and forms of drugs. For instance, Prohibition caused a striking drop in the production and sale of beer, while that of hard liquor increased as bootleggers from Al Capone on down sought to maximize their profits and minimize the risks of detection. Similarly, following the Second World War, the enactment of anti-opium laws in many parts of Asia in which opium use was traditional—India, Hong Kong, Thailand, Laos, Iran—effectively suppressed the availability of opium at the cost of stimulating the creation of domestic heroin industries and substantial increases in heroin use. The same transition had occurred in the United States following Congress’s ban on opium imports in 1909. And when during the 1980s the U.S. government’s domestic drug-enforcement efforts significantly reduced the availability and raised the price of marijuana, they provided decisive incentives to producers, distributors, and consumers to switch to cocaine. In each case, prohibition forced switches from drugs that were bulky and relatively benign to drugs that were more compact, more lucrative, more potent, and more dangerous.

In the 1980s the retail purity of heroin and cocaine increased, and highly potent crack became cheaply available in American cities. At the same time, the average potency of most legal psychoactive substances declined: Americans began switching from hard liquor to beer and wine, from high-tar-and-nicotine to lower-tar-and-nicotine cigarettes, and even from caffeinated to decaffeinated coffee and soda. The relationship between prohibition and drug potency was, if not indisputable, still readily apparent.

In turn-of-the-century America, opium, morphine, heroin, cocaine, and marijuana were subject to few restrictions. Popular tonics such as Vin Mariani and Coca-Cola and its competitors were laced with cocaine, and hundreds of medicines—Mrs. Winslow’s Soothing Syrup may have been the most famous—contained psychoactive drugs. Millions, perhaps tens of millions of Americans, took opiates and cocaine. David Courtwright estimates that during the 1890s as many as one-third of a million Americans were opiate addicts, but most of them were ordinary people who would today be described as occasional users.

Careful analysis of that era—when the very drugs that we most fear were widely and cheaply available throughout the country—provides a telling antidote to our nightmare legalization scenarios. For one thing, despite the virtual absence of any controls on availability, the proportion of Americans addicted to opiates was only two or three times greater than today. For another, the typical addict was not a young black ghetto resident but a middle-aged white Southern woman or a West Coast Chinese immigrant. The violence, death, disease, and crime that we today associate with drug use barely existed, and many medical authorities regarded opiate addiction as far less destructive than alcoholism (some doctors even prescribed the former as treatment for the latter). Many opiate addicts, perhaps most, managed to lead relatively normal lives and kept their addictions secret even from close friends and relatives. That they were able to do so was largely a function of the legal status of their drug use.

But even more reassuring is the fact that the major causes of opiate addiction then simply do not exist now. Late-nineteenth-century Americans became addicts principally at the hands of physicians who lacked modern medicines and were unaware of the addictive potential of the drugs they prescribed. Doctors in the 1860s and 1870s saw morphine injections as a virtual panacea, and many Americans turned to opiates to alleviate their aches and pains without going through doctors at all. But as medicine advanced, the levels of both doctor- and self-induced addiction declined markedly.

In 1906 the first Federal Pure Food and Drug Act required over-the-counter drug producers to disclose whether their products contained any opiates, cocaine, cannabis, alcohol, or other psychoactive ingredients. Sales of patent medicines containing opiates and cocaine decreased significantly thereafter—in good part because fewer Americans were interested in purchasing products that they now knew to contain those drugs.

Consider the lesson here. Ethical debates aside, the principal objection to all drug legalization proposals is that they invite higher levels of drug use and misuse by making drugs not just legal but more available and less expensive. Yet the late-nineteenth-century experience suggests the opposite: that in a legal market most consumers will prefer lower-potency coca and opiate products to the far more powerful concoctions that have virtually monopolized the market under prohibition. This reminds us that opiate addiction per se was not necessarily a serious problem so long as addicts had ready access to modestly priced opiates of reliable quality—indeed, that the opiate addicts of late-nineteenth-century America differed in no significant respects from the cigarette-addicted consumers of today. And it reassures us that the principal cause of addiction to opiates was not the desire to get high but rather ignorance—ignorance of their addictive qualities, ignorance of the alternative analgesics, and ignorance of what exactly patent medicines contained. The antidote to addiction in late-nineteenth-century America, the historical record shows, consisted primarily of education and regulation—not prohibition, drug wars, and jail.