A new study suggests that smoking cannabis just once as a teenager is enough to alter the structure of the brain.
Scientists found that smoking cannabis before the age of 14 can lead to significantly altered brain development.
Lead scientist Professor Hugh Garavan said people would likely “assume that one or two joints would have no impact on the brain”.
Scientists scanned the brains of 46 teenagers who admitted to smoking cannabis once or twice and compared them to others who had not smoked it.
Teens who smoked cannabis had an excess in grey matter in areas of the brain linked to emotion and memory.
The Daily Telegraph’s Science Editor, Sarah Knapton, wrote: “Although more brain cells might seem beneficial, in fact the developing teenage brain at this stage should be pruning cells as it prepares for adulthood”.
‘Persistent brain change’
The grey matter was found in areas of the brain known to be stimulated by cannabis use.
Sir Robin Murray, Professor of Psychiatric Research at King’s College London said further research was needed.
He said: “The question of whether cannabis use causes brain changes is an extremely important one given the worldwide increase in use of cannabis”.