Research on medical marijuana is hampered by federal regulations that tightly restrict supplies for studies. But there is a growing body of studies, much of it supportive of the drug’s medical usage, though some of it cautionary. Given the intense politics involved, it’s true, as Abrams puts it, that “you can find anything you want in the medical literature about what marijuana does and doesn’t do.’’

The tide seems to be turning in favor of wider medical use of marijuana. The Obama administration announced in March that it will end the Bush administration’s practice of frequently raiding distributors of medical marijuana. Thirteen states, including Vermont, Rhode Island, and Maine, now allow medical use of marijuana, according to Bruce Mirken, spokesman for the Marijuana Policy Project, which advocates legalization of pot. Last week, however, New Hampshire Governor John Lynch vetoed legislation that would have legalized medical marijuana in that state.

“Every day I see people with nausea secondary to chemotherapy, depression, trouble sleeping, pain,’’ he says. “I can recommend one drug [marijuana] for all those things, as opposed to writing five different prescriptions.’’

Some, like David Evans, special adviser to the nonprofit Drug Free America Foundation of St. Petersburg, Fla., applaud the government’s view, saying marijuana has not gone through a rigorous US Food and Drug Administration approval process.

The culture wars over marijuana, for recreational and medical use, have been simmering for decades, with marijuana (cannabis) still classified (like heroin) as a Schedule I controlled substance by the US government, meaning it has no approved medical use. (There is a government-approved synthetic form of marijuana called Marinol available as a prescription pill for treating nausea, vomiting, and loss of appetite, though advocates of the natural stuff say it is not as effective as smoked pot.)

With marijuana, however, “I can at least leave the dark room,’’ she says, “and it makes me eat a lot of food.’’

Duda has always had migraines. But they got much worse 10 years ago after two operations to remove life-threatening aneurysms, weak areas in the blood vessels in her brain. None of the standard drugs her doctors prescribe help much with her post-surgical symptoms, which include nausea, vomiting, loss of appetite, and pain on her left side “as if my body were cut in half.’’

But marijuana, says the 48-year-old Ware resident, is the only thing that even begins to control the migraine headaches that plague her nine days a month, which she describes as feeling like “hot, hot ice picks in the left side of my head.’’

Marcy Duda, a former home health aide with four children and two granddaughters, never dreamed she’d be publicly touting the medical benefits of “pot.’’

With that in mind, here’s an overview of what the research says about the safety and effectiveness of using marijuana to treat various ailments.

Pain: Marijuana has been shown effective against various forms of severe, chronic pain. Some research suggests it helps with migraines, cluster headaches, and the pain from fibromyalgia and irritable bowel syndrome because these problems can be triggered by an underlying deficiency in the brain of naturally-occurring cannabinoids, ingredients in marijuana. Smoked pot also proved better than placebo cigarettes at relieving nerve pain in HIV patients, according to two recent studies by California researchers. Marijuana also seems to be effective against nerve pain that is resistant to opiates.

Cancer: The active ingredients in cannabis have been shown to combat pain, nausea, and loss of appetite in cancer patients, as well as block tumor growth in lab animals, according to a review article in the journal Nature in October 2003. But there’s vigorous debate about whether smoking marijuana increases cancer risk.

Some studies that have looked for a link between cancer risk and marijuana have failed to find one, including a key paper from the University of California-Los Angeles and the University of Southern California published in 2006. “We had hypothesized, based on prior laboratory evidence, including animal studies, that long-term heavy use of marijuana would increase the risk of lung and head and neck cancers,’’ said Hal Morgenstern, a coauthor and an epidemiologist at the University of Michigan School of Public Health. “But we didn’t get any evidence of that, once we controlled for confounding factors, especially cigarette smoking.’’

Research published by a French group this year and by Kaiser Permanente, a California-based HMO, in 1997 came to a similar conclusion.

But a state health agency in California, the first state to legalize marijuana for medical use in 1996, recently declared pot smoke (though not the plant itself) a carcinogen because it has some of the same harmful substances as tobacco smoke. The active ingredient in marijuana can increase the risk for Kaposi’s sarcoma, a common cancer in HIV/AIDS patients, Harvard researchers reported in the journal Cancer Research in August 2007. And British researchers reported in May 2009 in Chemical Research in Toxicology that laboratory experiments showed that pot smoke can damage DNA, suggesting it might cause cancer.

The federal government’s National Institute on Drug Abuse says that it is “not yet determined’’ whether marijuana increases the risk for lung and other cancers.

Respiratory problems: Smoking one marijuana joint has similar adverse effects on lung function as 2.5 to 5 cigarettes, according to a New Zealand study published in Thorax in July 2007. A small Australian study published in Respirology in January 2008 showed that pot smoking can lead to one type of lung disease 20 years earlier than tobacco smoking.

Addictive potential: The National Institute on Drug Abuse says “repeated use could lead to addiction,’’ adding that some heavy users experience withdrawal symptoms such as irritability and sleep loss if they stop suddenly.

Mental effects: Cannabis may increase the risk of psychotic disorders, according to a 2002 study in the American Journal of Epidemiology. And the national drug abuse agency warns that “heavy or daily use of marijuana affects the parts of the brain that control memory, attention, and learning.’’ A study of 15 heavy pot smokers published in June 2008 in the Archives of General Psychiatry showed loss of tissue in two areas of the brain, the hippocampus and amygdala, regions that are rich in receptors for marijuana and that are important for memory and emotion, respectively.

Vaporizing vs. smoking: The push now among proponents of medical marijuana is toward inhaling the vapor, not smoking. Vaporizing is a safe and effective way of getting THC, the active ingredient, into the bloodstream and does not result in inhalation of toxic carbon monoxide, as smoking does, according to a study by Abrams published in 2007 in Clinical Pharmacology and Therapeutics.

Bottom line: From a purely medical, not political, point of view, my take is that if I had medical problems that other medications did not help and that marijuana might, I’d try it - in vaporized form.

Just as Marcy Duda does. “You use it as you need it. You can be normal. You can function,’’ she says. “I don’t get high. I get by.’’

© Copyright 2009 Globe Newspaper Company.