Smoking cannabis even occasionally as a teenager can damage your brain

Keep off the grass: Smoking even an occasional cannabis joint as a teenager can damage your brain, study warns

  • Experts from the US studied 1,192 teens from 596 families at two points in time
  • They found that cannabis use was associated with problems with verbal memory
  • This effect was found independent of both genetic and environmental factors
  • More data on marijuana’s effect on developing brains are needed, the team said 

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.

Teenagers’ brains can be damaged by smoking just the occasional joint of cannabis, as pictured — with a resulting loss in cognitive function — a study has warned

‘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.

‘Valid empirical data must be available to inform policy and public health decisions, including how cannabis use may affect the developing brain,’ Professor Ellingson said

‘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.


Cannabis is an illegal Class B drug in the UK, meaning possession could result in a five year prison sentence and those who supply the drug face up to 14 years in jail.

However, the drug is widely used for recreational purposes and can make users feel relaxed and happy. 

But smoking it can also lead to feelings of panic, anxiety or paranoia.

Scientific studies have shown the drug can alleviate depression, anxiety and stress, but heavy use may worsen depression in the long term by reducing the brain’s ability to let go of bad memories.

It can also contribute to mental health problems among people who already have them, or increase users’ risk of psychosis or schizophrenia, according to research.

Marijuana can be prescribed for medical uses in more than half of US states, where it is used to combat anxiety, aggression and sleeping problems. Researchers are also looking into whether it could help people with autism,eczema or psoriasis.

Cannabis oil containing the psychoactive chemical THC, which is illegal in the UK, is claimed to have cancer-fighting properties, and one 52 year-old woman from Coventry says she recovered from terminal bowel and stomach cancer by taking the drug.

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