Medical marijuana has been legal in Maine for almost 20 years. But Farmington physician Jean Antonucci says she continues to feel unprepared when counseling sick patients about whether the drug could benefit them.

Will it help my glaucoma? Or my chronic pain? My chemotherapy’s making me nauseous, and nothing’s helped. Is cannabis the solution? Patients hope Antonucci, 62, can answer those questions. But she said she is still “completely in the dark.”

Antonucci doesn’t know whether marijuana is the right way to treat an ailment, what amount is an appropriate dose, or whether a patient should smoke it, eat it, rub it through an oil or vaporize it. Like most doctors, she was never trained to have these discussions. And, because the topic still is not usually covered in medical school, seasoned doctors, as well as younger ones, often consider themselves ill-equipped.

Even though she tries to keep up with the scientific literature, Antonucci said, “it’s very difficult to support patients but not know what you’re saying.”

As the number of states allowing medical marijuana grows — the total has reached 25 plus the District of Columbia, including Oregon and Washington — some are working to address this knowledge gap with physician training programs. States are beginning to require doctors to take continuing medical education courses that detail how marijuana interacts with the nervous system and other medications, as well as its side effects.

Though laws vary, they have common themes. The role of doctors is often to certify that patients have an ailment that marijuana may treat. But many say that, without knowing cannabis’ health effects, even writing a certification makes them uncomfortable.

“We just don’t know what we don’t know. And that’s a concern,” said Wanda Filer, president of the American Academy of Family Physicians and a practicing doctor in Pennsylvania.

This medical uncertainty is complicated by confusion over how to navigate often contradictory laws. While states generally involve physicians in the process by which patients obtain marijuana, national drug policies have had a chilling effect on these conversations.

The Federation of State Medical Boards has tried to add clarity. In an Aug. 9 JAMA editorial, leaders noted that federal law technically prohibits prescribing marijuana, and tasks states that allow it for medical use to “implement strong and effective … enforcement systems to address any threat those laws could pose to public safety, public health, and other interests.”

That’s why many doctors say they feel caught in the middle, not completely sure of where the line is now drawn between legal medical practice and what could get them in trouble.

In New York, which legalized marijuana for medicinal purposes in 2014, the state health department rolled out a certification program last October. (The state’s medical marijuana program itself launched in January 2016.) The course, which lasts about four hours and costs $249, is part of a larger physician registration process. The state estimates 656 physicians have completed the required steps. Other states have contacted New York’s Department of Health to learn how the training works.

Pennsylvania and Ohio are developing similar programs. In Massachusetts, doctors who wish to participate in the state medical marijuana program are required to take courses approved by the American Medical Association. Maryland doesn’t require training but encourages it through its Medical Cannabis Commission website, a policy followed in other states.

Physicians appear to welcome such direction. A 2013 study in Colorado found more than 80 percent of family doctors thought physicians needed medical training before recommending marijuana.

Some advocates worry that doctors may find these requirements onerous and opt out, which would in turn thwart patients’ access to the now-legal therapy, said Ellen Smith, a board member of the U.S. Pain Foundation, which favors expanded access to medical cannabis.

Education is essential, given the complexity of how marijuana interacts with the body and how little physicians know, said Stephen Corn, an associate professor of anesthesiology, perioperative and pain medicine at Harvard Medical School. Corn also co-founded The Answer Page, a medical information website that provides educational content to the New York program, as well as a similar Florida initiative. The company, one of a few groups to offer education on medical marijuana, is bidding to supply information for the Pennsylvania program.

“You need a multihour course to learn where the medical cannabis works within the body,” Corn said. “As a patient, would you want a doctor blindly recommending something without knowing how it’s going to interact with your other medications?”

But many say the science is too weak to answer these questions. One reason: the federal Drug Enforcement Administration classifies marijuana as a schedule I drug, the same as heroin. This classification makes it more difficult for researchers to gain access to the drug and to gain approval for human subjects to participate in studies. The White House rejected a petition to reclassify the drug in a less strict category, though federal authorities say they will start letting more facilities grow marijuana for the purpose of research. (Currently, only the University of Mississippi can produce it, which advocates say limits study.)