“There's a lack of scientific evidence right now for anyone to be able to state exactly how much dosage an individual needs,” said Dominick Zurlo, who directs New Mexico’s Medical Cannabis Program. Given barriers to robust science, he said, it’s the people working in the medical marijuana field and acquiring experience who “are going to be the people who have the best information.”

Thirty-three states plus Washington, D.C., now allow medical marijuana. At least 2 million Americans are registered medical marijuana users, according to data from 26 states, meaning the nationwide number is likely higher. Millions more use hemp-derived CBD, which is now legal in some forms and omnipresent, and does not have the “high” of marijuana.

State dispensary rules vary enormously, according to numerous interviews with state medical marijuana programs, experts and advocates. More than half the states with medical cannabis allow budtenders to help patients choose products to address anything from back pain to chemotherapy side effects. Other states require the dispensaries have pharmacists, doctors or a nurse practitioner on site, or on call — but those health professionals may not have a full picture of the patient’s medical history, medications and treatments.

And unless a patient brings it up, or their regular doctor asks, a patient’s care team may not know about their marijuana use, or whether a patient is using it in addition to, or as a substitute for, a prescribed treatment. The internet is full of unproven claims about marijuana being nature’s magical treatment for everything from cancer to diabetes.

An employee lines up cannabis products at Essence Vegas Cannabis Dispensary after the start of recreational marijuana sales began on July 2017 in Las Vegas, Nevada. | Ethan Miller/Getty Images

All this is unfolding amid rapidly growing public acceptance of marijuana. Americans now view cannabis as much less harmful than alcohol, tobacco or e-cigarettes, according to a recent poll from POLITICO and Harvard’s T.H. Chan School of Public Health. That survey was done amid the outbreak of vaping-related illnesses, which has been linked to an additive in marijuana, mostly from the black market.

Even as public opinion shifts, states have adopted a variety of regulatory approaches. Some are strict. For instance, in Minnesota, only a licensed pharmacist can suggest products at retail locations; in Pennsylvania, it must be a pharmacist or other licensed medical professional at the dispensary. Maryland lets budtenders give general information about medical cannabis, but only physicians, pharmacists or nurse practitioners employed by the shops can provide more specific advice.

Louisiana’s program requires that specially registered physicians fax their recommendations directly to a marijuana pharmacy, which dispenses the products.

In many more states like Arkansas, New Jersey and Illinois, rules are laxer and budtenders can recommend products. That concerns some doctors, who worry their patients may be getting advice from someone behind the counter with limited knowledge of medicine — or the patient.

Yet many physicians, while wary of the dispensaries, steer clear of talking to their patients about a substance they believe is still inadequately tested and that they worry comes with political, legal and ethical landmines. Even physicians who are generally on board with cannabis are divided over how much advice they should be giving, at least until there are more widely accepted prescribing guidelines.

At the same time, some doctors are now focused heavily on certifying patients for state marijuana cards, or are incorporating marijuana more heavily into their practice.

For Dr. Matthew Mintz, primary care is still the core of his practice in Bethesda, Md. But now he spends about 20 percent to 25 percent of his time conducting 30-minute evaluations to determine if patients meet Maryland’s criteria for medical marijuana.

Mintz used to send those patients to dispensaries for advice on products and doses to try. But as a physician, he said, that bothered him. “I don’t say, 'Hey, Mr. Jones, you have [high] cholesterol, go to CVS and ask the pharmacist what to take.'” So, he started learning more about medical marijuana and writing down his own recommendations for the patients to take to a dispensary.

But many physicians still see a bridge too far between their offices and the dispensaries.

“That's what holds a lot of other doctors back because they are like, ‘you mean, I'm going to send my patient into a dispensary? And somebody with no medical background is going to guide them on what they should use or not use,’” said Dr. Patricia Frye, who operates Takoma Park Integrative Care in Maryland, where the services include teaching patients about cannabis and certification. She said federal restrictions have “really done a lot of damage in terms of keeping doctors or nurse practitioners or health care providers in the loop.”

“Many of these patients’ doctors and nurses and pharmacists are uncomfortable having these sorts of conversations with their patients,” said Paul Armentano, deputy director of the National Organization for the Reform of Marijuana Laws, a pro-legalization advocacy group. “The burden ends up being thrust upon those who work in the cannabis industry to respond to their patients’ questions.”

That’s left many budtenders learning what products, strains and doses to recommend through anecdotes from their patients to their own personal experiences and research they can find online. Some states require training for workers, and dispensaries can also set up their own programs, since they can’t turn to the federal government to regulate professional education about a product that’s still illegal.

“Our goal is education, so people can make informed decisions,” said Stephanie Kahn, the co-owner of the Takoma Wellness Center, a family-owned business which does employee training beyond the short course Washington, D.C., requires. She gives out her card to new patients, telling them they can email her at any time. She wants them to be comfortable — and she wants to know if they’re not.

It was a budtender who helped Tessa, of California, find relief from debilitating pain from severe endometriosis and a litany of other health problems. Nearly three years ago, she asked her doctors about trying medical cannabis. Their answer: Go for it, but we can’t help. (She asked that only her first name be used because she didn’t want her employer to know about her marijuana use.)

She found a doctor who spent about five minutes with her, at a cost of $45, and certified her for a card. At a dispensary, Tessa found a budtender who also suffered from endometriosis — and Tessa said her recommendations helped tremendously.

“I no longer worry about my work being impacted by my health, and I no longer worry about not being a responsible mom,” said Tessa, who responded to a POLITICO reader survey on medical marijuana. She’s kept her multiple doctors in the loop; they’ve watched her progress with interest.

Budtenders say they recognize they walk a fine line, delicately navigating the divide between traditional medicine and a federally illegal substance — and avoiding making blatant or irresponsible claims about marijuana.

Colorado has legalized marijuana for both recreational and medical use. So in Denver’s LoDo Wellness Center, recreational customers shop in one room of the store. A separate, nearly identical room provides a private space for medical patients to open up and seek advice. The staff is careful about talking about what might help — without overpromising, said Adam Segalis, a manager there.

“On the medical side, it's never been like, 'we're going to cure what your issue is,'” said Segalis, Instead they talk about what might help, and what’s recommended.

“We’re not doctors,” he emphasized, as customers — mostly there for legal weed — flitted in and out of the busy shop on a bustling Denver strip.