It’s becoming increasingly obvious that legalizing marijuana consumption was a colossal public-health blunder.

A good part of the evidence comes from south of the border, where several states legalized pot much earlier than Canada. This has allowed time for robust scientific follow-up — follow-up that is beginning to reveal a frightening picture.

Colorado legalized medical marijuana in 2012, and recreational use in 2014. One result is that emergency hospital visits by adolescents with marijuana-related symptoms have jumped from 84 a year in the pre-legal era, to 500 in 2018.

More troubling still, many of these teens exhibited signs of mental illness, including psychosis, depression and early-onset schizophrenia. There were also numerous cases of repeat vomiting.

Now the minimum age for purchasing the drug in Colorado is 21, or 18 if the patient has a medical certificate. Yet most of the kids being admitted to hospital are younger.

The obvious conclusion, and hardly a surprise, is that governments can set the age of consumption wherever they wish, and youngsters will still get their hands on the stuff.

Moving on, the cost of legal marijuana in Canada is now almost 50 per cent higher than the illicit version. According to Statistics Canada, the average price of a legal gram last year was $9.70, versus the black-market price of $6.51.

Now supposedly, one of the benefits of legalization was that it would drive drug traffickers out of business. But how is that going to happen, when the illicit stuff is much cheaper?

Answer: It isn’t. That same StatCan report found consumers are still buying more than twice as much of their stash from street vendors than from government-approved suppliers.

To be fair, there is a possible rejoinder here. It has taken longer than anticipated to get the necessary regulations in place. It might be argued that once a public-sector regime is fully implemented, prices could come down.

Yet from the beginning, various studies have found that regular users say they will continue to buy from black-market vendors they trust, even if a legal product were available.

In short, one of the most frequently claimed benefits for legalization — that it would de-fund drug gangs — hasn’t materialized so far, and might never occur.

That raises a third problem. In its 2018 budget, the B.C. government projected marijuana revenues of $200 million over three years. That figure has now been reduced to $68 million.

Other provinces, along with the federal government, have also revised their estimates downward.

But that should concern us. If you’re a cash-strapped administration, and sales aren’t where you’d like them to be, will you still play honest broker? Or will you ease up on the regulations and turn a blind eye to dubious behaviour so the revenues increase?

Now that the realities have begun to emerge, every one of the pro-legalization arguments is in doubt. Except, that is, the medical case, where the evidence of harm is overwhelming.

I don’t expect our governments to back down without a fight. The lure of a new cash source is just too appealing.

So here is a proposal. Let the B.C. Health Ministry contract with a research outfit — say, the Michael Smith Foundation in Vancouver — to examine the downstream health effects of marijuana legalization.

Run a five-year study at several of the province’s hospitals, looking for an increase in ER visits by teens with symptoms of psychosis once legal marijuana becomes readily available.

And if, as I’m willing to bet, a meaningful increase is found? Then shut down the entire legalization project, or 10 years from now we’ll be spending millions encouraging British Columbians to keep off the grass, just like we do with tobacco.

Except it will, of course, be too late by then.