On a sunny afternoon last August, a dozen women from Balfour Senior Living, in Louisville, Colorado, boarded a bus for a field trip to a marijuana dispensary. One used a walker, one was hooked up to an oxygen tank, and another wore a linen suit and jewelry. All were told to wear hats while walking from the bus to the dispensary door. “The sun is our enemy,” one said.

Joan Stammerjohn, who is eighty-four, said she’d joined the group because she’s had chronic pain in her legs, and has been on OxyContin for ten years. “I’d like to get off it,” she said. Others said they had ailments like arthritis or back pain, but didn’t want to disclose their names because they believe marijuana is still stigmatized. “We’re travelling incognito,” one said. “I’m excited. I came to open my mind—I want to know the latest things. I hope this won’t be in the paper, though. We’ll have a crowd coming to Balfour, thinking this is the coolest place.”

Filing inside the Ajoya dispensary, they were overwhelmed by display cases filled with pills, tinctures, edibles, jars of green flower clumps, vape pens, oils, patches, and creams. As they listened to budtenders suggest what to use for pain, arthritis, or sleep, a ninety-two-year-old bowed her head and slowly, slowly, started slumping against the counter. “Are you all right?” I asked. She fainted to the floor. A staff member knelt beside her as she regained consciousness. Paramedics arrived, but a half hour later, the woman, smiling, walked out the door with a hundred and twenty dollars worth of products.

Seniors are America’s fastest-growing population of new cannabis users. Ten thousand people turn sixty-five each day, according to the Pew Research Center, and more and more are trying the drug for their health and well-being. Even conservative politicians are warming to the idea. John Boehner, the sixty-eight-year-old former Speaker of the House, who in 2011 said he was “unalterably opposed” to the legalization of marijuana, recently made news by announcing that he was joining the board of Acreage Holdings, which distributes cannabis across eleven states. His “thinking on cannabis” had “evolved,” he tweeted.

In Louisville, the week before the field trip, there had been a lecture at Balfour by Joseph Cohen, D.O., the founder of Holos Health, which advises people on medical cannabis. The talk drew an overflow crowd of two hundred, with people standing against walls and spilling into the hallway. “The first thing older folks say when they enter our office is, ‘I don’t want to get high,’ ” Cohen said. He explained that there are two primary compounds in cannabis: THC, which is psychoactive, and CBD, which is not. “So CBD is a great solution for elders,” he said. “I took a little CBD before this talk, to make sure I stay calm.”

Cohen is seventy-one, with a long, gray ponytail and a beard. He recommends CBD for age-related diseases, such as Parkinson’s, dementia, osteoarthritis, and chronic inflammation. “CBD has twenty times the anti-inflammatory power of aspirin and two times the power of steroids,” he said. Since cannabis is federally illegal, none of his claims—or those made by any other clinician—can be supported by double-blind studies on humans, the gold standard in medical science. But in February a peer-reviewed study of almost three thousand patients in Israel, the first of its kind, showed that cannabis can be safe and effective for seniors, and lead to decreased use of pharmaceuticals, including opioids. In the study, published in the European Journal of Internal Medicine, almost ninety-four per cent of patients reported improvement in their condition, with their pain level reduced by half.

For Cohen, who practiced obstetrics and gynecology for thirty years, such results speak to the power of the endocannabinoid system, which regulates many body processes, such as nerve signalling, reproduction, and the immune system. “When I went to medical school, we didn’t know about the endocannabinoid system,” he said. “We knew about THC because we’d light up between classes.” The audience laughed. “We’re wired for this plant,” he continued. He explained that the body makes endocannabinoids—chemicals similar to THC and CBD—which lock onto receptors found throughout the body, especially in the brain. “Receptors are not found in the body because there is a plant out there that will trigger them,” Raphael Mechoulam, the Israeli biochemist who discovered THC, in 1964, said. “Receptors are present because the body makes compounds that activate them.”

Two major groups of seniors are turning to cannabis. The first, like the women on the field trip, have never tried marijuana and are drawn to its alleged health benefits. The second are boomers who “smoked dope” in the sixties and seventies, giving it up when they became focussed on careers or raising kids. An attorney I know in Los Angeles, who didn’t want his name disclosed, recently returned to the drug after developing acute pain in his joints. At seventy-one, he was diagnosed with polymyalgia rheumatica, an inflammatory autoimmune disease. His doctor put him on prednisone. This decreased the pain but had unpleasant side effects, including insomnia, and required him to give up his passion for fine wine.

When he began hearing that CBD was anti-inflammatory, he secured a medical license and went to a dispensary. “I was shocked,” he said. “The last time I was smoking grass, you bought a baggie filled with sticks and seeds from some shady character.” At the dispensary, he saw products labelled with the names of strains and the percentages of THC and CBD they contained. “The twenty-something budtenders became my sommeliers,” he said. “They’re as knowledgeable as wine stewards at the best L.A. restaurants.” He found a strain, Bubba Kush, that helped him sleep, and gradually started experimenting with other strains, finding new and enjoyable effects.

Another boomer I talked to is a former high-school art teacher, in Boulder, who wanted to try CBD for anxiety. After receiving strains with high amounts of the chemical from her daughter, in Seattle—Colorado growers were breeding the plant to increase THC instead—she started making her own oil from the plant. Her kitchen looked like a scene from “Breaking Bad.” (“Breaking Bud,” as she put it. ) The oil relieved her anxiety, and she shared it with friends, asking them to report their responses. One said it improved her arthritis; another said it helped with acid reflux. About forty per cent felt no effect. This confirmed what’s generally acknowledged: people respond differently to the same sample of cannabis. “You have to be your own chemistry set,” she said.

Cannabis’s appeal isn’t universal; it's still stigmatized in some communities. Sue Taylor, a seventy-year-old retired Catholic-school principal, never smoked pot while raising her three sons, and many in her Oakland community, she said, saw it as “a hardcore drug that got their young men in jail.” The incarceration rate of African-Americans for drug charges is nearly six times that of whites, despite a similar rate of drug use. When one of Taylor’s sons called to say he was studying at Oaksterdam University, which offers training for the cannabis industry, she flew to Oakland to “save him from drugs.” But she was persuaded of pot’s medical value after doing some research, visiting senior care homes, and working at Harborside dispensary, where she saw patients’ conditions improve after cannabis treatment.

Taylor is now a commissioner on aging in Alameda County, and said she is one of two people in California certified to train physicians and nurses in medical cannabis. She speaks at churches and senior centers. “In the beginning, they’ll sit, frowning, with their arms folded across their chests,” she said. “I tell them I’m not trying to convince anyone, I’m only here to educate you about the health benefits.” This summer, she plans to open iCANN Berkeley, a dispensary and wellness center, in a historically black neighborhood, which will cater to seniors. “Seniors are the most vulnerable population we have,” she said. “People think they can give them a pill and not worry if it’s gonna kill them because they’re almost dead anyway.”