Teenagers’ brains can be damaged by smoking just the occasional joint of cannabis — with a resulting loss in cognitive function — a study has warned.
US experts studying adolescent siblings found the early use of marijuana impacts the brain in a way that cannot be explained by genetic or environmental factors.
Cannabis users were more likely to suffer from verbal memory issues — resulting in problems recalling things read or heard — the team noted.
‘We wanted to expand our understanding of whether cannabis use is related to lower cognitive functioning,’ said paper author and psychiatrist Jarrod Ellingson of the University of Colorado School of Medicine.
‘There’s a large body of evidence that cannabis use is linked to cognitive functioning, but we know that cannabis use is not isolated from other important risk factors.’
‘That was the primary motivation behind this study, in which we compared siblings to account for many of these risk factors.’
Such factors, the researchers explained, included such environmental risks as peer group influence, parental behaviour and socioeconomic status.
In the study, Professor Ellingson and colleagues studied 1,192 teens from 596 families living in either Denver or San Diego at both the ages of 17 and later at 24.
By focusing their study on siblings — one of whom in each family was chosen for what the researchers refer to as ‘delinquent behaviours’ — the team were able to assess whether genetics factors play a role in cannabis use and its cognitive effects.
‘More work needs to be done to determine how cannabis use is related to cognitive functioning and we hope that our study can help inform future study designs,’ said Professor Ellingson.
‘These studies are particularly important because cannabis is becoming more potent and more accessible as states [in the US] legalise its recreational use.’
In Colorado, for example — where the research was conducted — cannabis was made legal in 2014, a move which has led to high rates of tourism to the state for both medicinal and recreational use of the drug.
‘Valid empirical data must be available to inform policy and public health decisions, including how cannabis use may affect the developing brain,’ Professor Ellingson added.
The full findings of the study were published in the journal Addiction.