Few people know the perils of drug abuse better than a 55-year-old former schoolteacher whose job it used to be to teach that very topic--which is why it's particularly ironic that she's a cocaine addict today. More than 30 years ago, Gwen--who prefers to keep it to one name when discussing her addiction--spent her days teaching in the Virginia school system and drafting the schools' drug-and-alcohol-abuse curriculum. She spent her nights researching the subject firsthand.

"I started using alcohol and pot in college," she says. "Then I turned to sniffing cocaine and freebasing. By the time I began teaching, I was spending big-time money. My body knew that I got out of school at 3:30 every day, and then I'd have to go out and get my drugs."

Today Gwen spends most of her time far from Virginia, living in New York City and attending regular sobriety meetings in the Odyssey House ElderCare treatment program in East Harlem. It's not how she envisioned her retirement. "I never thought the drug-abuse classes I taught applied to me," she says. "But here I am."

She's hardly alone. Of the more than 75 million baby boomers who came of age in the 1960s and '70s, millions experimented with drugs during their impressionable teenage years, and millions went on to enter middle age--and are now headed into their senior years--with decades-long addictions. Hard numbers are not easy to come by, but older addicts are clearly a growth sector in the drug-recovery industry. There are an estimated 1.7 million Americans over age 50 addicted to drugs, according to the Substance Abuse and Mental Health Services Administration (SAMHSA), a division of the Department of Health and Human Services. By 2020 SAMHSA expects the number to reach 4.4 million. Already an ongoing federal study has found that the number of older Americans seeking help for heroin or cocaine abuse roughly quadrupled from 1992 to 2002. Odyssey House, which was founded to treat younger addicts, now has a separate division, with both inpatient and outpatient facilities, to deal specifically with older users.

What makes the problem especially hard for seniors is that the wages of drug abuse are cumulative. A lifetime of recreational chemistry also means a lifetime of neglect of overall health--as a recent morning meeting at Odyssey House illustrated. There were too many canes in evidence for a group so comparatively young--the legacy of joints wrecked by years of undertreated diabetes--and too many bad hearts and bum livers and vascular systems fighting hypertension. "This is the first generation to have a high incidence of using recreational drugs," says SAMHSA epidemiologist Joseph Gfroerer. "All this puts them at risk for problems."

But why did those baby boomers stay aboard the drug carousel when so many millions more climbed off? And what exactly have 40 years of experimental pharmacology done to them? It would not have been possible--much less ethical--to recruit subjects when the 1960s drug circus got started, send them off for four decades of substance abuse and bring them back for study. But now that the ad hoc longitudinal experiment those aging boomers have been conducting on themselves is reaching its endgame, addiction experts are pouncing on what the doctors and psychiatrists treating the abusers are learning. What they uncover may help not only the surviving victims of the early drug years but younger users as well.

Of all the drugs the boomers have used, perhaps the four most notorious have been marijuana, hallucinogens, cocaine and heroin. Researchers have devoted enormous effort to studying those drugs' long-term effects. The results have been decidedly mixed.

MARIJUANA The so-called demon weed turned out to be a lot less devilish than advertised. The popular image of the goofy, smoky slacker notwithstanding, a 2003 study in the Journal of the International Neuropsychological Society found that even among regular users, there is no proof that pot causes irreversible cognitive damage. Memory does get cloudy, and learning new information does get harder, but those effects fade if the user does kick the habit. The drug may also diminish libido and fertility. (So much for its promised free-love properties.) And as with any intoxicating chemical, pot use can become chronic and compulsive, crowding out room for much else. "If you came to our adolescent program and saw the 16-year-old kids whose lives have become unmanageable as a result of pot use, you'd understand it's addictive," says psychologist Peter Provet, president of Odyssey House. "But a lot of people who use pot don't become addicts."

Scientists haven't settled on whether repeated chestfuls of unfiltered marijuana smoke increase the risk of pulmonary disease and cancers of the mouth, throat and lungs. Although a recent study out of UCLA says no, practitioners in the field disagree. "There's certainly strong if not definitive evidence that long-term smokers take in a lot of particulates and carcinogens," says Dr. Robert Raicht, medical director of Odyssey House.

HALLUCINOGENS Things are trickier when it comes to LSD and its hallucinogenic kin, but reports suggest that most '60s trips ended relatively benignly. The most rigorous studies of hallucinogens have been conducted not on boomers, who used the drugs intermittently and furtively, but on Native American populations for whom consumption of the hallucinogen peyote is part of their cultural and religious fabric. In November researchers from the McLean psychiatric hospital outside Boston released a five-year study that found no cognitive or psychological problems among Native American regular users, some of whom even performed better on psychological tests than those with minimal substance use. It's certainly too much to say that every peyote user emerges undamaged by the drug, and the lead researcher on the study, Dr. John Halpern, takes care to stress that his findings apply only to the Native American groups he studied.

LSD and mescaline, which are often whipped up in unpoliced labs in uncontrolled ways, present different problems. The condition that the experts call HPPD (hallucinogen persisting perception disorder) and that users call flashbacks is a very real problem. But Halpern says it is relatively rare, striking mostly people who use LSD specifically. But there are other risks too. Some trips have ended catastrophically, with suicides or fatal accidents. In other cases, the disaster was not physical but emotional. "There were a lot of people who decompensated into major mental illness," says Dr. Charles Grob, a professor of psychiatry at UCLA's school of medicine. "But you could make the case that these were people who were vulnerable to begin with."

COCAINE The coke party started late for most boomers--not until the 1980s--but when it hit, it hit hard. Even cocaine apologists admit that the drug is dangerously addictive and sometimes lethal. Coke-triggered strokes and heart attacks--both of which can occur in people with no known cardiovascular disease--are the real deal, caused by the sudden elevation of blood pressure and spasms of vessels. "The damage can be done suddenly and acutely," says Raicht, "or slowly and chronically."

Whether periodic cocaine use develops into disabling addiction can be something of a crapshoot. "There's a tendency for most people who have any kind of stake in conventional life to modulate their use and not let it get out of hand," says Craig Reinarman, a sociologist at the University of California at Santa Cruz and a co-author of two books on cocaine. For most people, he says, the breaking point for cocaine use is about an eighth of an ounce a week. But that's just a very general rule, and for many people, the threshold can be lower. And when it comes to crack--crystallized and smoked instead of snorted--addiction, often from the first use, is much harder to avoid.

HEROIN Easily the most lethal of the gang of four, heroin frequently hooks users for the rest of their lives, unless it simply kills them first. One long-term study, published in May 2001 in the Archives of General Psychiatry, followed 581 male heroin users from 1962 to 1997. Nearly half the subjects were dead by the time the study ended. Of those still alive, many were self-medicating with multiple other illicit drugs or alcohol and 67% smoked cigarettes. Not surprisingly, heroin users suffer from a wide range of medical ills, including hypertension, liver and pulmonary diseases and HIV. But the most common cause of death from heroin is overdose, with 22% of the subjects in the long-term study dying that way. Some of the health problems associated with heroin come from the impurities it is cut with. Overdoses often spring from an uncut batch that is unexpectedly pure.

The ultimate impact of any of those drugs, of course, depends on the users. No one has yet been able to tease out the precise mix of genetics, temperament and environment that makes one person a recreational user and another a lifelong addict, but clearly there is no single cause. "There are inherited components, hormonal components, psychosocial variables such as poverty," says Provet. And then, of course, there is mere opportunity--something the '60s provided in abundance.

"That was the era," says Evelyn, 56, an Odyssey House graduate and an addiction counselor there. "If the drugs hadn't been so available, I wouldn't have been apt to go looking for them."

As drug users mature, geriatric biology and life circumstances tend to tighten the drugs' hold. Reduced body mass, slower metabolism and less efficient kidneys and liver mean that the same quantity of drug hits harder and stays in the body longer. Older users who think they're keeping their doses fixed are thus, in effect, steadily increasing them. What's more, the loss of a spouse or job or merely the boredom of retirement could tip the nonuser into experimentation and the borderline user into full-blown addiction. Moses, 57, never touched heroin until 2001, when his wife died. But when he picked it up, he got hooked fast. "I missed my wife. I was lonely," he says. "I didn't want to live, but I didn't have the nerve to put a gun to my head."

For the seniors who do get clean--and the millions more who will need to in the years to come--there are a few factors that drive recovery. Seeing peers die of addiction certainly scares some straight. So too do late-life worries about the legacy one is going to leave. "You get to a point when you think about having a dignified end," says Jon Roberts, another Odyssey House veteran who is now a counselor. "You think about family reunification, about giving back through community service, about having spent your life as more than an addict."

It's rare for teenagers of any generation to think that far ahead, never mind the cohort that reached adolescence at the height of the drug boom. It may be impossible to slow the demographic conveyor belt that's going to dump so many of them into the senior population with a habit they picked up during their summers of love. But it's not too late for them to shake it off, achieving the peace in the last chapters of their lives that the drugs promised them in the first.