(Astrid Riecken/The Washington Post)

Susan Okie is an assistant clinical professor of family medicine at Georgetown University School of Medicine, a poet, and a former medical reporter and science editor at The Washington Post.

A Doctor’s Case for Medical Marijuana

By David Casarett

Current. 289 pp. $27.95

‘Does medical marijuana ‘work’?” That question, posed in an illuminating new book by David Casarett, a hospice physician and researcher at the University of Pennsylvania, sounds simple and turns out to be anything but.

The short answer is that it depends on the symptom or problem being treated, on the physiology of the patient using it, on the mode of drug delivery (a joint? a brownie? a vapor pen? a beer?) and on various other factors. A small but growing trove of research suggests that for some symptoms — insomnia, nausea, certain kinds of pain, muscle spasms, perhaps even the disabling anxiety of post-traumatic stress disorder or the agitation often experienced by people with Alzheimer’s — medical marijuana does work. And for some other conditions, marijuana or drugs based on some of its active ingredients appear promising.

“It’s starting to look to me like marijuana might offer real medical benefits,” Casarett acknowledges halfway through “Stoned,” noting that he embarked on the book project believing he’d find little evidence of weed’s effectiveness.

That’s potentially good news for people living in states where medical marijuana is legal — currently 23, plus the District — but it’s only half the picture. Research has also identified risks clearly associated with marijuana use. Casarett reports worrisome evidence of a link between marijuana use and psychosis, and somewhat weaker findings suggest that it may increase users’ chance of developing schizophrenia. It can also cause addiction in some people, since it lights up the brain’s pleasure circuitry in essentially the same way as alcohol, cigarettes or cocaine — although a user’s risk of becoming addicted probably depends on her genetic makeup, frequency of use and the strength of the marijuana product being inhaled or ingested.

Much of the marijuana sold in the United States today contains five to 10 times more THC (short for tetrahydrocannabinol, the ingredient that makes people high) than the weed smoked in the 1970s. Smoking or “vaping” potent marijuana or hashish delivers a rapid bolus of THC into the bloodstream, and the resultant swift rise, crest and fall of the drug’s level in the brain probably enhances its addictive potential. Withdrawal symptoms can occur in heavy or frequent users, and may include anxiety, insomnia, decreased appetite, aggression, depression, and physical symptoms such as stomach pain or headache.

Some studies have also found subtle structural changes in the brains of heavy marijuana users, fueling worries about possible permanent effects on learning and memory. On the other hand, some of the theoretical concerns long cited by researchers about marijuana’s potential for damaging organs have not been borne out by studies. In particular, marijuana — despite containing many of the same components as tobacco — has not been found to damage the lungs or cause lung cancer in longtime smokers. In one study, smoking it even improved lung function in people with asthma. And, although smoking it can lower a user’s blood pressure, increase heart rate and make blood more likely to clot, so far it hasn’t been shown to lead to heart attacks or strokes. Still, Casarett warns that people with diabetes, high blood pressure or other risk factors should be warned of the possibility of such an event, and he cautions that marijuana should not be used during pregnancy.

Statistically, the most life-threatening danger of marijuana — both to users and to the general public — is probably the herb’s well-documented impairment of driving skills. Recent use slows a driver’s reaction time, reduces the brain’s ability to focus and worsens performance when faced with multiple tasks. Studies indicate that driving while stoned approximately doubles the risk of an accident. Moreover, the effects persist for hours, and there’s currently no reliable sobriety test for users. Casarett advises: “If you’re thinking of getting high and then driving a car . . . Don’t. Just don’t.”

Although his methodical parsing of the scientific evidence makes the book slow going at times, Casarett spices things up with a hands-on approach to investigative reporting. Not only did he seek out and interview numerous patients who said their symptoms had been relieved by marijuana when nothing else had worked, he experimented on himself. By my count, he describes trying marijuana in four different forms, testing their ability to relieve what ails him as well as their effect on his consciousness. His first trial — a marijuana poultice applied to his sore knee by a local healer during a hiking trip in Nepal — was a failure: little or no pain relief, since the herb’s active ingredients can’t get through skin unless the dose is dissolved in chemicals to make it pass through more easily. The second, a sip of marijuana-infused beer, “is a little like drinking Kool-Aid out of a Wellington boot that’s been used extensively for barnyard labor,” Casarett reports.

Hoping to quaff the herb in a tastier beverage, he downed half a bottle of marijuana-infused red wine. The result: He was tipsy but felt no buzz, even though two pounds of weed went into each barrel of the vintage. Casarett explains why: The herb’s active ingredients are poorly absorbed from the digestive tract, then are chemically modified in the liver, reducing their ultimate effect on the brain. Smoking or inhaling vapor is a much more efficient way to deliver marijuana’s components to the body than eating pot.

For his final trial, Casarett tested the ability of smoking marijuana to relieve the muscle spasms he had been suffering as a result of a recurrent lower-back condition. Sitting on his patio, he smoked part of a joint. The good news: His back muscles began to loosen up. The bad news: He saw his patio chairs dancing and seemed to hear the voices of air traffic controllers coming from inside his house. His first-hand account of weed-induced hallucinations underscores the book’s message that marijuana’s effects are produced by dozens of chemicals whose levels vary in different strains of plants, and that choosing a particular strain or dose and predicting how it will work in a particular patient is difficult, requiring both expert advice and trial and error.

But with the medical use of marijuana expanding and additional states likely to legalize the practice, Casarett argues that it’s time to test and standardize the quality of the products being dispensed to patients, and to require clinics and dispensaries to educate would-be consumers more thoroughly about the herb’s potential benefits and risks. Posing as a patient at two different marijuana clinics, he encountered one that fulfilled those responsibilities and one that fell far short. In the future, he predicts, researchers will explore how the plant’s several dozen cannabinoids — the active ingredients — affect the brain, immune system and other organs, and may create new, targeted drugs as a result of those discoveries.

In the meantime, he believes that well-informed patients who want to try marijuana should be allowed to weigh the risks against the hoped-for benefits. “Why don’t we give the public a role in research?” he asks. “Let them see what happens. And then let their experiences guide the design of rigorous trials that reflect the wisdom of the crowd.”

Anyone considering whether to use marijuana for a medical condition will find this book a valuable introduction to becoming an educated consumer.