Smoking cannabis for three years in your teens can ruin long-term memory.

Teenagers who smoke cannabis for just three years could be damaging their long- term memory, researchers have warned.

Participants in a study who had used the drug daily for around three years in their teens had an abnormally shaped hippocampus – a region of the brain vital to memory – by the time they were in their early 20s.

They also performed around 18 per cent worse in long-term memory tests than individuals who had never touched the drug.

The results were uncovered using sophisticated brain-mapping scans taken two years after they stopped smoking cannabis.

Professor John Csernansky, from Northwestern University in the US, who co-led the research, said: ‘The memory processes that appear to be affected by cannabis are ones that we use every day to solve common problems and to sustain our relationships with friends and family.’

The study is one of the first to suggest that abnormally shaped brains in heavy cannabis users are directly related to memory impairment.

The longer a participant had been exposed to cannabis the more misshapen their hippocampus appeared on scans.

This could mean brain regions related to memory may be more susceptible to the effects of the drug the longer the abuse occurs.Dailymail reported.