Too legit to quit? Medical marijuana dispensaries are filling storefronts and making it safer for patients with legitimate needs. But cities are challenging the propriety of health care's latest strain.

• Author: Ryckman, Lisa

On a sunny Saturday in January, 72 people paid $250 each to hear Dana May--aka "Professor Marijuana"--divulge the secrets of successful cannabis cultivation.

The self-proclaimed best grower on the planet, May tells the group he can produce in 43 days what typically takes four to five months, from start to finish, seed to weed. He has three rules, and the first of which--and possibly most important--is the KISS principle: Keep It Simple, Stupid.

"Less is more," May says. "And define your goals. If you give this plant what it wants when it wants it, it will do amazing things."

A photo flashes up on the screen: It's May holding the fruit of his labor, a pampered plant bushy enough to be a small Christmas tree. An appreciative murmur ripples through the room. This is what many of the attendees--mostly middle-aged, mostly male--are here to learn: how to jump into the market for medical marijuana (also known as MMJ or medical cannabis), arguably the state's fastest-growing cash crop.

It's a startup like no other: simultaneously booming and hamstrung, besieged on one side by ever-increasing demand for a limited supply and on the other by opposition from law enforcement, legislators and residents who view medical marijuana dispensaries as more akin to liquor stores or porn shops than pharmacies. Legitimized by voters nearly a decade ago but still illegal under federal law, medical marijuana remains saddled with a "Reefer Madness" image that could only be overcome by a doozy of a marketing campaign, if then.

"This is a controversial business, and government is one of its most hostile enemies," says Denver attorney Robert Corry, one of the state's best-known go-to guys for patients, growers and dispensary owners who find themselves crosswise with the law. "Give them any rope, and they will hang this industry. And there's plenty of rope."

Compassion is at the heart of the matter: Amendment 20 to the Colorado Constitution legalized medical cannabis for use by people suffering from a variety of debilitating illnesses, many of whom say it has weaned them from narcotics and given them a new quality of life. With the recommendation of a physician, they can either grow their own or obtain it from someone they designate as a "caregiver."

At last count, more than 19,000 people had been registered as patients with the state Department of Public Health and Environment, and there are at least another 19,000 in the pipeline, according to state Sen. Chris Romer, the Denver Democrat who has been trying to craft some kind of dispensary regulation on the state level. "There are those of us who believe there will eventually be 60,000," he says.

The amendment is directed at patients; it has nothing to say about dispensaries, which were under the public radar until several things happened. In 2007, the courts threw out a state health department rule that imposed a five-patient limit per caregiver; last summer, the department declined to reinstate it. And a year ago, U.S. Attorney General Eric Holder announced that the Justice Department would no longer go after people who followed state law for using, prescribing or distributing medical marijuana.

Suddenly, a good deal of the risk went out of this risky business, and a crop of dispensaries popped up seemingly overnight. By some counts, there are more medical marijuana dispensaries--200 or more--in the greater Denver metro area than there are Starbucks.

Buying medical marijuana, however, is generally more complicated than picking up a grande latte. Patients need a doctor's recommendation, which many physicians have been reluctant to supply because of fear of possible repercussions from medical boards or the government. Despite that, more than 800 different doctors have signed for patients, according to the state Department of Public Health and Environment.

"I'm willing to do so because the evidence I have studied is so strongly supportive of the use of cannabis in a great many situations," says Dr. Alan Shackelford, a Denver internist, whose practice includes Amarimed, which evaluates people who think cannabis might help them.

"This is not a bunch of stoner kids trying to get around the law," he says. "The vast majority are productive adults for whom this is an important part of their medical regimen."

Efforts to regulate on the state level might well focus on the doctor-patient relationship, Romer says, including putting an end to doctors...