"American Spirits," the wonderful exhibit about Prohibition that's been whetting thirsts at the Minnesota History Center for the past two months, is timed to coincide with last month's 80th anniversary of the repeal of the alcohol-banning 18th Amendment to the U.S. Constitution — right?

I'm certain its timing has nothing to do with the fact that a bill to allow doctors to legally prescribe marijuana for palliative purposes is awaiting action by the 2014 Legislature. Or that on Jan. 1, Colorado became the nation's first state to legalize marijuana for recreational use, with Washington state soon to follow and more pot-legalization initiatives in the works in a smattering of cities and states.

I didn't even spot the word "marijuana" on my recent visit to the Prohibition exhibit. But the final line on the exhibit's last poster could be read as relevant to the cannabis debate that's gaining steam in Minnesota and the nation. By attempting a nationwide ban on the production, sale and distribution of alcohol, the poster said, "Americans also learned … that the appetites of individuals could not be easily governed."

That lesson certainly applies to pot. It's the most commonly used illegal drug in the country. By one estimate, one out of three Americans have used it at some point in their lives. (Personal disclosure: I'm not among them.)

Intentionally or not, the History Center's Prohibition recap reveals a number of parallels to marijuana. Like alcohol, cannabis was legal to consume in most of the United States in the 19th century. It was legal with a doctor's prescription in many places in the early 20th century. Like alcohol, marijuana's reputation suffered because of its association with immigrants and nonwhite people. Like alcohol, it was finally outlawed by federal action that has proved to be quite ineffective in containing its consumption or crimping its availability. (This exhibit tidbit is telling: New York City alone had a jaw-dropping 32,000 ­alcohol-serving speakeasies when Prohibition ended.)

But Americans were quick to sour on Prohibition, particularly on the anti-beer version pushed through Congress in 1919 by Minnesota's own very sober Rep. Andrew Volstead of Granite Falls. (A fierce-looking Volstead, dubbed "Prohibition's public face," glares from a title page in the latest issue of "Minnesota History," the Historical Society's quarterly journal.)

After a dozen years and the onset of the Great Depression, the nation's desire to get the taps flowing and the booze industry hiring and paying taxes again was overwhelming. It took only eight months for the then-requisite 36 states to ratify Prohibition's repeal after Congress sent it to the states in 1933. Restarting beer sales, which had been halted by the Volstead Act rather than by the 18th Amendment, was among the first acts of the 1933 Congress and new President Franklin Roosevelt.

The federal ban on marijuana started less dramatically, as a tax, and didn't come to full flower until 1970, when "flower children" were distressing their elders with their fondness for weed. Not long afterward, Minnesota was one of 10 states in the 1970s to reduce criminal penalties for possession of small amounts of pot, rendering a first-time offense akin to a traffic ticket.

The cannabis ban has been slowly cracking for nearly two decades. Twenty states and the District of Columbia now allow doctors to prescribe "medical marijuana" use.

A group of hardy advocates has long been trying to add this state to that list. They plan to try again this year to convince the Legislature that it's cruel to bar sick and dying people from legal access to a substance they say provides more relief from misery than any alternative. They'll cite studies that show that in many respects, cannabis presents fewer risks to public safety and health than do two legal substances, tobacco and alcohol.

What has to be interesting, and a little frightening, to these persistent souls is that this year, they're getting new questions, such as: "Why not follow Colorado? Why not go for full legalization?"

That's not the plan, insists lobbyist Chris DeLaForest, an attorney and former Republican legislator whose clients include the Marijuana Policy Project. "There is no secret plan to do a more general legalization bill," DeLaForest stressed last week. "The sole focus of our bill is to protect doctors when they decide to prescribe this product and patients when they use it."

His desire to confine the 2014 legislative debate to medical marijuana is understandable. That proposal has proved to be controversial enough. Every major law enforcement organization is on record opposing any relaxation in the marijuana ban — a phalanx that then-Gov. Tim Pawlenty cited when he vetoed a medical-marijuana bill in 2009. Dakota County Attorney James Backstrom, a fellow who knows how to get attention, is outspoken on the subject, arguing that more teen usage and more impaired driving will result if Minnesota does anything to make pot use more prevalent.

But as DeLaForest notes, no similarly organized opposition has surfaced from the state's medical community. Through years as a lobbyist on the issue, "I've never once debated a person trained in medicine," he said.

My hunch: Allow doctors the power to outlaw only one of three commonly used substances — tobacco, alcohol and marijuana — and marijuana wouldn't be their choice.

Opposition to marijuana, medical and otherwise, seems to be melting away in other quarters. A March 2013 poll by Public Policy Polling found 65 percent of all Minnesotans — including 49 percent of Republicans — support legalizing marijuana for medical purposes. Among 18- to 34-year-olds, support hits a whopping 87 percent.

Meanwhile, a number of national polls in recent months have found majority support among Americans for going Rocky Mountain High — legalizing pot, à la Colorado. A CNN/Opinion Research poll released last week put national support for medical marijuana at a politically irresistible 88 percent.

Public opinion polling was in its infancy just as Prohibition ended. There's no way of knowing how the ban on alcohol would have polled in 1933. But here's another hunch: If Gallup, Pew and the rest had been around to ask, their findings would have looked like the poll numbers accumulating lately about pot.

Note to the Minnesota Historical Society: Please prepare a seminar for state lawmakers on the post-Prohibition era. I think they'll soon benefit from history's guidance about how to convert a problematic substance from "controlled" to "regulated."

Lori Sturdevant is a Star Tribune editorial writer. She is at lsturdevant@startribune.com.