The path to David Casarett's new book began when one of his patients at Penn Medicine's Wissahickon Hospice asked him if medical marijuana could help her.

As usual with such questions, he scoffed, telling her the drug was still illegal and there was no evidence to support its use.

His patient, a retired English professor, pushed him for more information. He discovered that there was indeed research, and she knew more about it than he did. "She was tough," he said.

He promised he would look into it for her. That was about a year and a half ago. The result of his quest - Stoned: A Doctor's Case for Medical Marijuana - was published last week.

The retired professor has since died, but her questions turned Casarett, who is in charge of hospice and palliative care at Penn, into a more nuanced thinker about the controversial weed. He is not as much an advocate as the book's subtitle implies, but he thinks medical marijuana is "a reasonable option for some patients." He also would like to see more research, plus careful regulation and product testing.

His journey of enlightenment included the expected interviews with pot researchers, but also entertaining, wryly described visits with a variety of everyman users and amateur weed experts. He learned firsthand how hash - a refined form of marijuana - is made. He sipped wine steeped with marijuana, pronouncing it a "tragic waste of 2,000 joints." He witnessed the effectiveness of the Volcano, a marijuana vaporizer. He tried a pot-based ointment for an aching knee in Nepal. It was not much help. And, in the only instance of admitted law breaking, he tried one joint (delivered by a lawyer, mind you) on his patio in Mount Airy. It might have helped his back spasms a little, but he saw his furniture move and heard what sounded like the voices of air traffic controllers coming from his living room.

He also staged an amusing-but-scary driving test with a self-medicated brain-tumor patient named Jeff. Instead of orange traffic cones, they used bananas. Many ended up mashed.

Casarett said he thought the book might be "useful" because so much of the debate around medical - and recreational - marijuana is about politics rather than the risks and benefits of a powerful plant.

Medical marijuana is legal in 23 states, including New Jersey, and the District of Columbia.

However, marijuana is still under debate in Pennsylvania, where the Pennsylvania Medical Society opposes a Senate bill that would allow marijuana use in patients with any of 15 conditions, including cancer, Crohn's disease, and diabetes. A House bill has a shorter list.

Medical Society vice president Charles Cutler, a Norristown internist, said the organization wants stronger evidence - along with changes in federal rules making it easier to do research - before making marijuana more widely available. The group is also concerned about side effects.

Two drugs that contain active ingredients from marijuana - dronabinol and nabilone - have been approved by the Food and Drug Administration.

Kevin P. Hill, a Harvard University addictions doctor who also produced a book on marijuana this year (Marijuana: The Unbiased Truth about the World's Most Popular Weed), said the plant has 60 active ingredients, which might make it more effective for some patients than the approved drugs.

While he has concerns about the 9 percent of marijuana users who become addicted, he supports legalizing medical marijuana. Hill, who wrote an article for the Journal of the American Medical Association last month, said there is good evidence for using marijuana for nausea and vomiting after chemotherapy and to stimulate appetite in people with wasting illnesses such as HIV. Those are what the FDA-approved drugs are for. Beyond that, there is also good evidence for chronic and neuropathic pain, as well as spasticity associated with multiple sclerosis. He said the data are building for epilepsy.

Casarett did not attempt to evaluate the quality of studies that tested marijuana in various forms. He wanted the book to be readable for the general public. He also thinks that patients who have already failed to get relief from FDA-approved drugs are not as interested in placebo-controlled, double-blind studies as scientists are. "If you're that desperate for relief, weak evidence is better than no evidence," he said.

He says marijuana is "probably" helpful for insomnia and might alleviate symptoms of anxiety and post-traumatic stress disorder. He is "worried and sad" when he hears patients are using marijuana instead of chemotherapy for cancer.

He says it's important for patients and their doctors to understand how the drug works and what the risks could be. Among those are addiction, psychosis, and, possibly, heart attack and stroke. Everyone, he said, should be cautioned not to drive while high.

He doesn't recommend marijuana, but he acknowledges that some of his patients are already using it. "They should know what they're doing, and they should know the risks," he said.

He has just started a Kickstarter campaign for a crowd-sourced website, marijuanaresults.org, that will collect data from marijuana users about what they're using and how it's affecting their symptoms. He thinks it will be useful for the patients themselves, for others with similar illnesses, and for researchers trying to figure out what to study.

A soft-spoken 47-year-old with short, gray hair, Casarett seemed perplexed when asked if he had fun meeting the loopy or rough-edged characters in the book.

"The fun part really was having my assumptions [about medical marijuana] tested and blown away," he said.

Yet he remains "mystified" about why it is such a popular cause. He says it might appeal to people because they feel they have more control at a dispensary than at a pharmacy.

"There is some evidence," he said, "but there doesn't seem to be enough evidence to support this groundswell of enthusiasm."

Casarett, who puts medical marijuana in the "herbal remedy" category, thinks it will become less enticing as drug companies develop better competing medications.

215-854-4944@StaceyABurling