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By Ellie Zolfagharifard
PUBLISHED: 06:24 EST, 25 July 2013Daily Mail U.K.
Teenagers who regularly smoke cannabis suffer long lasting brain damage and are in much greater danger of developing schizophrenia. American researchers say the drug is particularly dangerous for a group of people who have a genetic susceptibility to the mental health disorder - and it could be the trigger for it.
Asaf Keller, of the University of Maryland School of Medicine, said the results highlight the dangers of teenagers smoking cannabis during their formative years.
The study, published in the journal Neuropsychopharmacology, exposed young mice to the active ingredient in marijuana for 20 days. It found that their brain activity was impaired, with the damage continuing into adulthood.
The past 20 years has seen major controversy about the long-term effects of marijuana, with experts divided over its long-term effects on teenagers. Previous research has shown that children who started using marijuana before the age of 16 are at greater risk of permanent brain damage, and have a significantly higher incidence of psychiatric disorders.
‘Adolescence is the critical period during which marijuana use can be damaging,’ said the study's lead author, Sylvina Mullins Raver, a PhD candidate at the University of Maryland School of Medicine.
‘We wanted to identify the biological underpinnings and determine whether there is a real, permanent health risk to marijuana use.’
The scientists began by examining cortical oscillations in mice. Cortical oscillations are patterns of the activity of neurons in the brain and are believed to underlie the brain's various functions. These oscillations are very abnormal in schizophrenia and in other psychiatric disorders.
The scientists exposed young mice to very low doses of the active ingredient in marijuana for 20 days, and then allowed them to return to their siblings and develop normally.
‘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.
‘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 repeated the experiment, this time giving marijuana to adult mice that had never been exposed to the drug before. Their cortical oscillations and ability to perform cognitive tasks remained normal, indicating that it was only drug exposure during the critical teenage years that impaired brain activity. ...