Univiersity of Tartu Professor Human Physiology Eero Vasar says that frequent and intensive use of cannabis changes several basic processes in the body, and triggers irreversible health damage.

From the point of view of brain development, an individual's age though to young adulthood is extremely critical, he said.

"At about five years of age, a process starts from the occipital lobe of the cerebral cortex and reaches the frontal lobe by the age of 20 during which the cerebral cortex grows thinner," Professor Vasar said, according to a university press release.

"The goal of thinning is the formation of normal neural circuits. If this process is affected by external influences like cannabis during this critical period, the person may develop serious disorders," he added.

Professor Vasar was joined by Associate Professor in Psychiatry Liina Haring and other medical researchers in the study, entitled "Drugs and Developing Brains".

The survey involved close to 5,000 Estonian people and assessed cannabis use among 16–45-year-olds, analyzing whether, and to what extent, the psychopathological symptoms of cannabis users and non-users differ.

Other studies have shown that young people using cannabis are 1.4 times more likely to develop depression, 1.5 times more likely to experience suicidal thoughts and 3.5 times more likely to attempt suicide compared with their non-cannabis using peers.

Around 9 percent of those who have tried cannabis in their lifetime become everyday cannabis users, while 30 percent of those who have used high-tetrahydrocannabinol (THC) products in the past year may develop an addiction to cannabis.

"This is four to seven times more likely for people who have started using these products before the age of 18, compared with those who started as adults," Professor Liina Haring said.

The recreational use of cannabis is nonetheless increasing in Estonia, as it is worldwide, the University of Tartu says.

The study found 43 percent of respondents had used the drug at some point in their lifetime, with the average age of first use being 17-18, though many younger users were also found.

"Of the 16-year-old cannabis users who participated in the survey, 14.6 percent of them had tried the drug by the age of 13 and 68 percent of them did so before the age of 16. These are significant proportions, given the detrimental effects of tetrahydrocannabinol (THC) acid in cannabis on the functioning of the maturing brain," Professor Haring said.

Links between cannabis use at a young age and behaviors on the schizophrenia spectrum, and the onset of a primary psychotic episodes, have been found by studies, along with emotional and cognitive disorders arising from regular cannabis use .

The findings of researchers of the University of Tartu align with previous studies, which say cannabis users are more likely to experience depression, sleep disorders, lack of motivation and disturbances of perception and thought.

Part of the problem is a widespread misconception of marijuana as being safe, perhaps in relation to its use in some jurisdictions for medicinal purposes, and its legalization in some parts of the world, including many U.S. states.

Young marijuana users often do not readily seek help when health problems occur, the study added.

Parents, healthcare and youth workers, teachers, experts and others should all join in the effort to make the detrimental effects of cannabis known to young people, the study found.

Cannabis possession in Estonia is a criminal offense if in large quantities, as is distribution, whereas possession of small amounts constitutes a misdemeanor offense, punishable by a fine.

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