Teenagers, who frequently smoke weed, suffer long-term brain damage and have a greater risk of developing schizophrenia, according to a study conducted by American researchers. The study is published in the journal Neuropsychopharmacology.

The findings particularly hold true for people who have a genetic susceptibility to the mental health disorder. The cannabis could activate the disorder.

Asaf Keller, of the University Of Maryland School Of Medicine, said the results reveal the possible dangers teens could face from smoking cannabis.

"Adolescence is the critical period during which marijuana use can be damaging,' said Sylvina Mullins Raver, the study's lead author. "We wanted to identify the biological underpinnings and determine whether there is a real, permanent health risk to marijuana use.'

For the study, the scientists exposed young mice to very low amounts of the active ingredient in marijuana for 20 days. They found that their brain activity was impaired, with the damage continuing into adulthood.

 "In the adult mice exposed to marijuana ingredients in adolescence, we found that cortical oscillations were grossly altered, and they exhibited impaired cognitive abilities,' said Raver, a PhD candidate at the University Of Maryland School Of Medicine. 'We also found impaired cognitive behavioural performance in those mice. The striking finding is that, even though the mice were exposed to very low drug doses, and only for a brief period during adolescence, their brain abnormalities persisted into adulthood."

The scientists conducted the experiment for the second time on adult mice. They gave the marijuana to adult mice that were never exposed to the drug before. They found that their cortical oscillations and the ability to perform cognitive tasks remained normal, which implied that when the brain is exposed to the drug during critical teenage years, it impairs brain function.

"We found that the frontal cortex is much more affected by the drugs during adolescence,' said Keller. "This is the area of the brain controls executive functions such as planning and impulse control. It is also the area most affected in schizophrenia."