You know things are shifting in America when Fortune magazine, the bible for business journalism, runs a cover story titled “Is pot already legal?”. You also know it when Barack Obama’s Department of Justice publishes a long-expected memo signalling that the federal government will no longer raid medical marijuana dispensaries if they are legal under state law. That happened formally this month.

It was not, moreover, a symbolic gesture. Marijuana for medical reasons — to tackle chemotherapy-induced nausea or Aids-related wasting or glaucoma, among other conditions — is now legal in 13 states, including the biggest, California. Next year, 13 more states are planning referendums or new laws following suit. Last week a California legislative committee held the first hearings not simply on whether medical marijuana should remain legal, but on whether all marijuana should be decriminalised, full stop. The incentive? The vast amounts of money the bankrupt state could raise by taxing cannabis.

Now look at the polling on the question. In 1970, 84% of Americans supported keeping marijuana illegal. Today, that number has collapsed to 54%. The proportion believing that marijuana should be legal has gone from 18% at the end of the 1960s to 44% today. On current trends, a majority of Americans will favour legalisation by the end of Obama’s first term. In the western states, 53% already favour legalising and taxing the stuff. Support for legalisation is strongest among the young — the Obama generation — but has climbed among self-described Republicans as well.

But the reality is already ahead of the polls. Take a trip, so to speak, to Los Angeles today, where one would be forgiven for thinking that marijuana was already legal. There are more than 800 marijuana dispensaries in the city — and an estimated 7,000 in the state of California as a whole (many times more than in Holland).

Getting a doctor’s recommendation for marijuana is easier than getting health insurance — just look at the ads in the papers, where a consultation costs about $200. The dispensaries range from the dime store to elaborate palaces of capitalist taste. Seminars are held for entrepreneurs who want to start a business selling medical cannabis. On display are sophisticated strains that can provide exquisitely tailored effects: some best for countering nausea, some for building appetite, others for going to sleep, others for staying alert or for watching movies or for general relaxation.

The concentration of THC, the active compound, is much higher than in the past. But since no one has ever overdosed on marijuana, it’s difficult to say why that matters. Yes, if someone has a history of mental illness, it’s not that smart to experiment with the cannabinoid receptors in the brain. But it isn’t smart for such people to take any drugs — or too much alcohol — for that matter. For most people, stronger pot merely translates into a need for less of it to get the same effect. Too much and you’ll likely nod off — and wake up later with no hangover. If pubs served pot rather than beer, crime rates would plummet.

Americans, for whom the use of marijuana is almost a rite of passage in most colleges, know all this. And at some point they stopped pretending otherwise. The past three presidents smoked marijuana in their earlier days, even if only one has openly written about it. (Obama, when asked the Clinton question — if he had inhaled — responded: “I thought that was the point.”) In an online press conference with his younger supporters, the first question was about whether legalising and taxing pot would be a good thing to help raise revenues. Obama laughed it off. With an annual deficit of more than a trillion dollars, he may not be able to laugh it off much longer.

The key to the shift has been the emphasis on marijuana’s medical properties. Human beings have used marijuana as medicine for millennia. It was once sold in the States by Eli Lilly, the pharmaceutical manufacturer. Allowing this compassionate use for a few soon revealed, accidentally, how harmless it is. It is not chemically addictive, although some mild withdrawal can happen if you are a regular pot-smoker and go cold turkey. Its side-effects are minimal compared with those of most authorised drugs for similar conditions. It is far less addictive than tobacco or alcohol. It leads to no measurable degree of antisocial behaviour, as is the case with, say, crystal meth or cocaine or heroin. Many of its users are successful, productive members of society who simply prefer it to alcohol as a relaxant in the evening or as a way to get through cancer treatment.

Denying Aids patients a tool to stay alive tips the balance. I have one friend who would never have been able to tolerate the medications that saved his life without it. That’s pretty persuasive stuff and lots of people have similar first-hand experiences. A gateway drug? Yes, many users of hard drugs smoked pot in the first place. But almost all started out with alcohol as well — and that is not illegal.

Of course, nothing is inevitable. The police still police it and hundreds of thousands of Americans — disproportionately black and poor — are in jail for it. Los Angeles’s failure to regulate adequately its hundreds of dispensaries may lead to connections with organised crime that could come back to delegitimise the whole thing.

I give it a couple of years to become a non-issue or to go into reverse. And my bet is that in a decade’s time, the banning of cannabis will seem as strange as the banning of alcohol. In the end, unnecessary prohibition undermines itself. And this time around, there are millions of cancer and HIV patients who are on the side of legalising and some truly desperate branches of government looking to see what they can tax next. In fact, I’ll go further: sooner rather than later, marijuana may be more acceptable than tobacco.

The need for taboos is eternal. But the object of the taboo is always shifting. The age of tobacco may be ending; and the millennium of marijuana may be about to begin.

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