IT was as if she woke up one day and decades of her life had disappeared.

Joyce, 52 and a writer in Manhattan, started smoking pot when she was 15, and for years it was a pleasant escape, a calming protective cloud. Then it became an obsession, something she needed to get through the day. She found herself hiding her addiction from her family, friends and co-workers.

“I would come home from work, close my door, have my bong, my food, my music and my dog, and I wouldn’t see another person until I went to work the next day,” said Joyce, who like most others in this article asked that her full name not be published, because she does not want people to know about her past drug use.

“What kind of life is that? I did that for 20 years.”

She tried to stop, but was anxious, irritable, sleepless and lost. At one point, to soothe her cravings, she took morphine that she found at her dying father’s bedside. She almost overdosed.

Two years ago, she checked into the Caron Foundation, a treatment center in Wernersville, Pa. Even there, she said, some other addicts — cocaine and heroin users or alcoholics — downplayed her dependence on marijuana.

“The reality is, I was as sick as them,” Joyce said. She now attends Alcoholics Anonymous, which is also open to drug addicts, and recently married.

Smoking pot, she said, “was a slow form of suicide.”

Marijuana, the country’s most widely used illicit drug, is typically not thought to destroy lives. Like alcohol, pot has been romanticized by writers and musicians, from Louis Armstrong to Bob Dylan, and it has been depicted as harmless or silly in movies like “Harold and Kumar.” And addiction experts agree, marijuana does not pose as serious a public health problem as cocaine, heroin and methamphetamine. The drug cannot lead to fatal overdose and its hazards pale in comparison with those of alcohol. But at the same time, marijuana can be up to five times more potent than the cannabis of the 1970s, according to the National Institute on Drug Abuse.

And this new more-potent pot and the growing support for legalization has led to an often angry debate over marijuana addiction. Many public health officials worry that this stronger marijuana has increased addiction rates and is potentially more dangerous to teenagers, whose brains are still developing. And officials say the movement to legalize marijuana — now available by prescription in 13 states — plays down the dangers of habitual use.

“We need to be very mindful of what we are unleashing out of a Pandora’s Box here,” said Dr. Richard N. Rosenthal, chairman of psychiatry at St. Luke’s-Roosevelt Hospital in Manhattan and professor of clinical psychiatry at Columbia University. “The people who become chronic users don’t have the same lives and the same achievements as people who don’t use chronically.”

More adults are now admitted to treatment centers for primary marijuana and hashish addictions than for primary addictions to heroin, cocaine and methamphetamine, according to the latest government data, a 2007 report by the Substance Abuse and Mental Health Services Administration.

Even though alcohol and opiates (which includes painkillers and heroin) are the two leading primary addictions, the percentage of those seeking treatment for marijuana addiction, compared with 10 years ago, has increased significantly to 16 percent in 2007 from 12 percent in 1997. The percentages of those seeking treatment for cocaine (13 percent of admissions in 2007) and alcohol addiction (22 percent in 2007) declined slightly.

Advocates for legalizing marijuana and some addiction specialists say these concerns are overwrought. The admissions data, they say, is deceiving because it was collected by government agencies that oppose legalization; 57 percent of those admitted for marijuana addiction treatment were ordered to do so by law enforcement. (The percentage of those ordered into treatment was lower for other drugs, except for methamphetamine. For alcohol abuse, 42 percent were ordered into treatment.)

Advocates and even some addiction specialists say cannabis is an effective treatment for medical and emotional problems, and can even help some battling addictions to harder drugs.

The risk of addiction, they say, is less problematic than for alcohol and other drugs. For instance, of the people who had used marijuana, only 9 percent became addicted, according to a 1999 study by the Institute of Medicine of the National Academies, a nonprofit research organization on science and health. Of those who drank alcohol, 15 percent became addicted. For cocaine, the figure was 17 percent, and heroin, 23 percent. (These are the latest figures from the institute; advocates and addiction experts said there were no more recent data available.)

“The word addiction is so fungible in our society, and cannabis just doesn’t fit that tidy definition, though it can be abused,” said Allen St. Pierre, executive director of the National Organization for the Reform of Marijuana Laws, a legalization advocacy group. “Science really has proven, if anything, that cannabis is likely one of the safest substances we can interact with.”

Many people can smoke marijuana every day without ill effects, advocates say, just as many casually drink wine in the evening.

These marijuana users do not meet the clinical definition of addiction, which includes an inability to stop using the drug, an uncontrollable obsession with it and increased tolerance. Javier V., a 24-year-old supervisor in an industrial park in Miami, said he has smoked pot regularly, without a problem, since he was 14. “After a busy day at work,” he said, “I come home, roll up a J and — I mean, it’s stress relief.”

Then there are people like Milo, 60, who recently attended his first Marijuana Anonymous meeting in Los Angeles. He said he started smoking pot at 13, and has struggled to quit.

He is also an alcoholic, he said, but has not had a drink since the early 1980s.

“I’m a pothead, a marijuana addict, a stoner, we call ourselves a million things,” he said. He is trying to quit, he said, because his girlfriend is threatening to leave him. Besides, the drug no longer alleviates his depression and anxiety.

“I’m losing things and people,” Milo said after the meeting. “I’m estranged from my children. I’ve lost two houses, and I’m living in my R.V., basically homeless.”

He added, “There are a whole lot of pieces, and I can’t get them together.”

Many addiction experts would say marijuana abuse has, at the very least, added to Milo’s problems. And the drug’s new potency has made the likelihood of addiction that much greater, public health officials say.

“It’s like drinking beer versus drinking whiskey,” said Dr. Nora D. Volkow, director of the National Institute on Drug Abuse, a government agency and a strong opponent of legalizing marijuana. “If you only have access to whiskey, your risk is going to be higher for addiction. Now that people have access to very high potency marijuana, the game is different.”

A 2004 study in the Journal of the American Medical Association suggested that the stronger cannabis is contributing to higher addiction rates. The study, conducted for the National Institute on Drug Abuse, compared marijuana use in 2001 and 2002 with use a decade earlier.

While the percent of the population using the drug remained stable during that time, dependence or abuse on the drug increased significantly, particularly among black and Hispanic men. Higher concentrations of delta-9-tetrahydrocannabinol, known as THC, the study said, was the likely reason for the growing dependency.

Dr. Volkow, who spearheaded federal research into treatment for marijuana withdrawal, had studied cocaine in the 1970s and early 1980s. Back then, she said, she was unsuccessful in winning grants to study cocaine addiction.

“People thought cocaine was a very benign drug,” she said.

Government statistics show the number of emergency room visits linked to the use of marijuana, which can lead to psychotic episodes and was cited in other medical emergencies, has risen significantly.

With marijuana, “it’s going to take some real fatalities for people to pay attention,” Dr. Volkow said. “Unfortunately that’s the way it goes.”

Only after the basketball player Len Bias died of a cocaine overdose in 1986, and the crack epidemic began, did the government start a campaign to warn of cocaine’s dangers.

Like any addiction, quitting pot can be daunting. Jonathan R. has been a member of Marijuana Anonymous in Los Angeles since the early ’90s, shortly after the 12-step program was founded. He has seen many members in meetings say they would rip up their medical marijuana cards, available in California and used to fill prescriptions for problems ranging from severe pain and discomfort from cancer, to headaches and insomnia.

But then, inevitably, he said, they secure another one, much like “an alcoholic who pours booze down the drain and then goes out to get another bottle.”

The difficulty in quitting has spurred psychologists and psychiatrists to debate whether “Cannabis Withdrawal Syndrome” should be in the next edition of the Diagnostic and Statistical Manual of Mental Disorders.

Yet, marijuana withdrawal is not nearly as severe as withdrawal from most other drugs. Giving up drinking can cause fatal seizures. Heroin users vomit and sweat for days; sudden withdrawal can be fatal.

In fact, some doctors specializing in treating addicts would rather prescribe marijuana for anxiety and insomnia than sleeping pills or Valium and Xanax, which are highly addictive.

“I see people every day dying from alcohol, stimulants and opiates,” said Dr. Matthew A. Torrington, an addiction specialist and clinical researcher at the University of California, Los Angeles. “Marijuana may be an up and comer, it may be transforming into something that will become a bigger problem in the future, but at the moment I don’t see that.”

Still, even one of Dr. Torrington’s patients, Jonathan James, has concerns about his own marijuana use. Mr. James, 50, a former choreographer, has been a regular pot smoker for 35 years.

He said smoking marijuana helped inspire some of his most original ideas. But Mr. James is afraid to stop smoking, even after kicking heroin and cocaine. When he stopped the harder drugs, he stayed off pot for six months. When he started again, he planned to smoke only a few times a week.

After a month or so, “I started smoking it more,” he said. “Two months later, I was smoking it in the morning, and four months later I was smoking all day.”

He said he would be more successful without pot.

“It keeps me back — from engaging in the dreams and aspirations I have,” he said. “I would like to feel I don’t need to take anything to feel better.”