One hundred years ago today, President Woodrow Wilson approved the Harrison Narcotics Tax Act, the US’s first national legislation designed to control the manufacture, import and supply of opium and cocaine. Francis Burton Harrison, a Democrat representative, did little more than give his name to the law. The heavy lifting was done by Dr Hamilton Wright, a zealous public health specialist who believed that opium was “the greatest curse which humanity has ever known”. After wildly exaggerating the scale of drug addiction in the US, with particular reference to alleged drug-induced depravity among certain ethnic groups, Wright drew up a Bill that effectively banned the sale of narcotics for recreational use. It sowed the seeds for the war on drugs as we know it today.

History almost demands that a law as portentous as the Harrison Act should have been the subject of anguished discussion and national controversy. In fact, the Congressional debate lasted only a few minutes and was not even mentioned in that day’s New York Times. The American public was more interested in arguing about the other great Progressive cause of the era – alcohol prohibition – than defending non-medical drug use, which almost everybody agreed was immoral.

The Harrison Act gave the medical establishment a monopoly over the supply of drugs. For a few years under the new regime, physicians made handsome profits selling opiates to addicts until the Supreme Court ruled, in March 1919, that addiction was not a legitimate medical problem. Almost overnight, 200,000 opiate habitués were deprived of a legal source of supply and, by 1930, a third of America’s prison population had been incarcerated for drug violations.

Three months after the Supreme Court ruling, the Treaty of Versailles brought an official end to the First World War and, thanks to a little noticed clause inserted by the American government, brought the international war on drugs to an unofficial start. Article 295 of the treaty obliged the belligerent nations to suppress the sale and import of opiates. Britain fulfilled its duty by making its wartime restrictions on the sale of drugs permanent with the Dangerous Drugs Act of 1920 (since superseded by the 1971 Misuse of Drugs Act).

Even before the Harrison Act, various statewide prohibitions had built the foundations for an illicit market characterised by harder drugs, higher prices, organised crime and street-dealing. At the start of the twentieth century, the typical American drug addict was either an elderly, middle class, female morphine addict or an opium smoker of Chinese descent. Both kept themselves to themselves. Under prohibition, the typical addicts were young, male heroin users gathering in the street and committing crime to fund their habit. It is no coincidence that the word "junkie" was coined in the early 1920s.

Before the Harrison Act, the typical drug – though potentially hazardous – was regulated, relatively pure and manufactured by legitimate businesses. Today, the typical drug is of unknown provenance, heavily adulterated and of variable strength. Before the Harrison Act, the typical drug dealer was a pharmacist or physician. Since the 1920s, he has been a member of a criminal underclass.

The Harrison Act allocated $150,000 for enforcement of the new drug laws – the equivalent of around $3m in today’s money. In 2009, the US government spent nearly $10bn on enforcement and a further $5bn on treatment and prevention.

What would they say, those men who drafted the Harrison Act, if they could see where a century of drug prohibition has left us? What would they make of America’s 2.5m prisoners, a quarter of whom are incarcerated for drug offences? How would the public health doctor Hamilton Wright, who died in 1917, view the world’s 4m people who contracted HIV as a result of sharing needles, or the 10m who contracted hepatitis C by the same method, or the 1.3m who contracted hepatitis B?

With their Progressive faith in the power of law to reform mankind, they would, I think, be surprised to hear that narcotics are still used at all, let alone that consumers have shifted from opium and patent medicines to methamphetamine, crack and heroin (largely for the convenience of the seller rather than the buyer). They would be appalled to see the widespread use of intravenous injection which was unknown before the 1910s. Above all, they would be astonished and disillusioned to find there are many more drug addicts and drug-related deaths than there had been in their day.

Five years after Wilson signed the Harrison Narcotics Tax Act, the 18th Amendment brought alcohol prohibition to the USA. Whatever else might be said about that "noble experiment", it came about after decades of intense debate over the "drink question" and was repealed after its failure had become manifest. By contrast, America slid into a century of drug prohibition in 1914 with barely a murmur, and no amount of crime, death and disease seems to be enough to bring about reform. Recent moves towards decriminalisation and legalisation in Portugal, Uruguay and a few US states offer some hope, but I would not bet against the war on drugs living to see its second centenary in 2114.