Americans spend roughly $25 billion a year on marijuana, according to the Harvard economist Jeffrey Miron, which gives some idea of the popularity of this drug. Eventually, we might be talking about a sizable sum of tax revenue from its sales as medicine, not to mention private investment and employment. A spokesman for the National Organization for the Reform of Marijuana Laws says hedge fund investors and an assortment of financial service firms are starting to call around to sniff out opportunities.

“We’re past the days when people call here to ask if marijuana will give men breasts,” says Allen St. Pierre, the executive director of NORML. “Now, the calls are from angel investors, or REITs — people who are looking for ways to invest or offer their services.”

What happens when pot goes legit? How does the government establish rules that allow the industry to flourish, but not run rampant? And given that this is all about medicine, what about doctors, some of whom have turned medical marijuana consultations into a highly lucrative specialty?

These and dozens of other questions are now being answered in cities like Boulder, an affluent, whole-grain kind of college town where the number of dispensaries — anywhere from 50 to 100, depending on whom you ask — is larger than the number of Starbucks and liquor stores combined. During a recent visit, it was clear that for every marijuana seller and physician who thinks that the rules are too strict, murky or fluid, there are others who can hardly wipe the smile off their faces.

“When I visited in September, I looked around and saw that there were only four dispensaries in Boulder, and they were all right on campus,” says Bradley Melshenker, co-owner of the Greenest Green and formerly a medical marijuana seller in Los Angeles. “We went into one and saw like 30 kids in the waiting room, and I thought: ‘This is crazy. We’ve got to come.’ ”

YOUR first foray into a medical marijuana center is slightly disorienting, like breathing underwater during your maiden scuba dive, or watching the Red Sox win the 2004 World Series. Everything in your past tells you that the experience is impossible, but at the same time, you know it is happening.

Forget the furtive transactions that have defined American pot dealing since the dawn of the dime bag. The best of Boulder’s dispensaries display their product in the sort of glass cases found in jewelry stores or high-end bakeries.