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Profile of a plant

What science does and doesn't tell us about the health benefits of cannabis.

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Cannabis sativa is a member of the family Cannabaceae — which also includes hops and the common hackberry tree — but longstanding disagreement exists over whether the genus includes more than one species or merely different varietals. (Though some maintain Cannabis indica is a separate species, most scientists now classify indica as a subspecies of Cannabis sativa.) Taxonomy aside, cannabis has been used by humans for millennia — for the versatile fibers of its stalks (hemp), the nutritional value of its seeds, and, of course, the chemical compounds found in its female flowers and leaves.

There are dozens of distinct cannabinoid molecules, two of which are especially significant. Tetrahydrocannabinol, or THC, is the primary agent responsible for getting you high. Cannabidiol, or CBD, is not psychoactive but nonetheless affects the brain in powerful ways. CBD appears to be effective in treating some forms of epilepsy, and the anecdotal evidence for its benefits is strong enough that many states resistant to legalizing medicinal cannabis allow very limited use of low-THC/high-CBD products (Oklahoma, Texas and Mississippi are among them). But psychoactive THC has its therapeutic applications as well.

On Jan. 12, the National Academies of Sciences, Engineering and Medicine released a landmark review of the scientific literature on the health impacts of marijuana use, examining the abstracts from over 10,000 studies published since 1999. Any such report comes with the qualification that research into human consumption of marijuana has been crippled by the substance's ongoing federal prohibition. That means the scientific data is limited, despite the fact that the drug is one of the most widely consumed in the world. "Unlike other controlled substances such as alcohol or tobacco, no accepted standards for safe use or appropriate dose are available to help guide individuals as they make choices regarding the issues of if, when, where, and how to use cannabis safely and, in regard to therapeutic uses, effectively," the report's overview states.

The National Academies report found "conclusive or substantial evidence" that cannabis or its derivatives are effective for treating chronic pain in adults, for relieving muscle spasms in individuals suffering from multiple sclerosis and for alleviating chemotherapy-induced nausea and vomiting in cancer patients. The report found "moderate evidence" the drug can help with sleep disorders and "limited evidence" it could benefit patients with post traumatic stress disorder, Tourette syndrome, social anxiety disorders and more. However, it found limited evidence against the effectiveness of cannabis for treating glaucoma or dementia, and no evidence in either direction for its effectiveness regarding a number of other medical issues, including cancer, irritable bowel syndrome, epilepsy, Parkinson's disease and treating addiction to more pernicious substances like opioids.

On the other side of the public health ledger, the researchers found "substantial evidence" that smoking marijuana regularly "is associated with more frequent chronic bronchitis episodes and worse respiratory symptoms," though they found evidence that it is not associated with an increased incidence of lung cancer or head and neck cancers. Evidence regarding a link with other cancers was inconclusive. The report also found substantial evidence that cannabis use was correlated with increased vehicular accidents, lower infant birth rates and the development of schizophrenia or other psychoses. It found limited evidence for a correlation with other harmful effects, from chronic obstructive pulmonary disease to various mental health problems.

To thousands of patients in Arkansas and elsewhere who say cannabis has helped them overcome or cope with a host of disorders, the National Academies report may sound frustratingly limited in scope. But science moves slowly by design (and even more so when federal law stands in its way), and the report's conclusions regarding the benefits of marijuana in reducing chronic pain, nausea and muscle spasms are monumental.

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