This interesting article I found on The Stars website here

 note that it says the THC level found in the 80s in Marijuana used to be 3 or 4%. Now it is more like 12 %.

“At age 17, sitting in the basement with friends smoking pot, Don Corbeil first noticed all the cameras spying on him. Then he became convinced a radioactive chip had been planted in his head. “I thought I was being monitored like a lab rat,” he explains.

It never occurred to him that marijuana could be messing with his brain. Corbeil had been smoking pot since he was 14, a habit that escalated to about 10 joints a day.

He started hearing voices and, at one point, Corbeil thought he was the Messiah. Police found him one day talking incoherently, and brought him to hospital, where he was eventually diagnosed with drug-induced psychosis.

Corbeil had dabbled in other drugs, such as acid and ecstasy. But marijuana was his mainstay.

When he went on anti-psychotic medication and off pot, the symptoms eventually stopped. But twice he tried smoking it again, and both times the demons sprung up. “Within 10 minutes, the voices started,” says Corbeil, now 20, of North Bay. “It was as if people had been in a box for a few years and then you take the lid off and they all want to talk to you.”

He slammed the lid back on the box — he swore off marijuana.

With good reason: Research in recent years has shown that marijuana can trigger psychosis in vulnerable individuals. But who exactly is at risk remains hazy.

Smoking marijuana is one of a messy mix of circumstances — genetics, stress, injury, age of first use — that likely predispose someone to psychosis.

“There seems to be a combination of risk factors. But nobody knows which combinations can be the triggers.” says Jean Addington, psychiatry professor at the University of Calgary and president of the International Early Psychosis Association.

Some studies suggest that youth in their early teens who become regular users — toking a few times a week — have double the risk five years later of paranoia, hallucinations and psychotic breaks.

While most studies have focused on cannabis and psychosis, researchers are also investigating the relationship between marijuana and other mental illnesses. In a survey of more than 14,000 Ontarians, Robert Mann, senior scientist at the Centre for Addiction and Mental Health found that people who use cannabis almost every day were twice as likely to have anxiety or mood disorders as non-users. The study, however, did not determine whether the drug prompted symptoms or was used to self-medicate.

And a McGill University study on rats last year found that injecting adolescents daily with small doses of synthetic marijuana led to depression-like and anxiety-like behaviours in a series of tests. Researchers also found that rats’ brains were altered long-term.

“We finally understand that marijuana is not the harmless substance we thought it was,” says Dr. Leonardo Cortese, chief of psychiatry at Windsor Regional Hospital.

No one is talking about the return of Reefer Madness, the 1930s film about cannabis use leading to death and destruction. The vast majority of pot smokers will not go psychotic.

But two recent developments have researchers particularly bummed about pot.

Imaging studies now show that crucial regions of the brain are still developing in the teen years, the very time many start smoking pot. After alcohol, marijuana is the teen drug of choice. More than 30 per cent of Ontario’s Grade 10 students reported cannabis use in the past year, according to CAMH.

And what they’re smoking is not their hippie dad’s doobie. Growers have bred more potent pot, more than doubling the amounts of Tetrahydrocannabinol, the psychoactive ingredient, and decreasing the cannabidiol, a protective ingredient.

About 3 per cent of the population will experience a psychotic episode from all causes. The rate, however, of cannabis-induced psychotic episodes is not clear.

“We’re just catching up to the effects of high-octane weed,” says Dr. James Kennedy, director of the neuroscience research department at CAMH. “We need new follow-up studies to see its effect on the population.”

While psychosis is rare, for the kid hearing voices, it is life-altering. Some are lucky and the symptoms stop when the drugs stop, but for many, the voices and hallucinations recur.

Social stresses such as family problems and emotional trauma contribute to the risk of psychosis, as do some biological factors, such as brain injury, says Addington. A family history of serious, persistent mental illness, particularly psychosis, ratchets up the risk too, but the genetic markers are by no means clear cut…

In the 1980s, the THC level in marijuana was about 3 to 4 per cent. In the last couple of years, says Det. Don Theriault of the Toronto Police, tests on marijuana show a 10 to 12 per cent THC level.

An estimated 20 per cent of Caucasians carry that COMT variant. That does not neatly translate into a one-in-five risk, however. “They could have several other genes that are protective. It gets complicated,” says Kennedy.

So what percentage is at risk of psychosis from marijuana?

Kennedy hesitates. This is not solid scientific ground.

“I’d guess 10 to 15 per cent would be at significant risk if they smoked a lot of marijuana, almost daily, in their teen years when the brain isn’t fully developed.”

It’s the brains front part, crucial in judgement and social perceptions that’s still under construction in the teen years. “The wiring, the circuits where the neurotransmitters flow and signal are still being laid down,” says Kennedy.

So does smoking pot permanently change or damage this still-maturing brain?

We’ll have that answer in two or three years, says Kennedy. Imaging studies tracking the growth of teens’ brains are looking at whether cannabis use alters the development, or permanently damages still-maturing brains.

It’s not only teens that may be vulnerable, however.

Ana Smith didn’t use marijuana regularly until her mid-20s, after she graduated from film school. “I’d stay home in the evenings with my cats, make tea and smoke weed,” says Smith, a Vancouver resident, now 39.

Then she started smoking during the day as well, first thing in the morning and through the afternoon, instead of writing screenplays. The only time she didn’t smoke was weekends, when she worked in a group home. She didn’t drink or do other drugs.

At first the voices in her head were pleasant. “They tricked me into thinking I was being discovered by Hollywood. It was a beautiful world for a couple of months.”

Then they turned evil, terrifying her. Smith spent four lost days just walking, sleeping on the streets. She finally checked herself into a hospital and was diagnosed as a paranoid schizophrenic.

Smith has no known family history of mental illness. But a geneticist told her she had inherited genetic frailties from both her parents. Smith had also been under a lot of stress. “I think pot tipped me over the edge.”

After the diagnosis, Smith kept smoking pot because the voices demanded it. She stopped two years ago and her mental health has improved. “Now I know it’s just the illness rearing its head,” she says.

Research suggests that only about 15 per cent of people who experience a first psychotic episode do not have another, says Dr. Suzanne Archie, clinical director of the Cleghorn Early Intervention in Psychosis Centre in Hamilton. For a large portion of that 15 per cent, the episode was probably due to drugs.

“It can be very tricky to figure out if it was substance-induced or if there’s an underlying psychiatric illness,” says Archie.

If the patient is off drugs for six months with no psychotic symptoms, Archie leans toward a substance-induced diagnosis.

But for the majority, those diagnosed with a psychotic illness, the big question is: Could it have been prevented if the cannabis had been avoided?

That’s impossible to know, researchers say.

“The marijuana could cause schizophrenia to come on sooner,” says Kennedy. “If it interacts with a not fully-developed brain it could create a more severe, a more disruptive version of schizophrenia.”

With schizophrenia, marijuana likely precedes psychosis, although some people may smoke to ward off early symptoms.

With depression and anxiety, clinicians face a chicken-and-egg dilemma: Did the pot help spark the symptoms, or was it used as an attempt to self-medicate?

“These cases are difficult to tease apart,” says Dr. Benjamin Goldstein, adolescent psychiatrist at Sunnybrook Hospital. He advises anyone feeling anxious or depressed to stay away from weed. “The effects of pot on them swing more steeply toward the risk end.”

 To read the full article see The Star website.