Cannabis damages young people’s ability to retain information and do well in class, a study suggests. File picture: Ted S. Warren/AP Photo.

Cannabis damages young people’s ability to retain information and do well in class, a study suggests.

Just a week after giving up the drug, participants aged 16 to 25 were far more likely to remember lists of new words than those still using it.

The memory test results provide yet more evidence for the damage cannabis does to developing brains.

The researchers, led by Harvard Medical School, said the drug may damage memory centres such as the prefrontal cortex. Lead author Dr Randi Schuster, of Harvard’s Centre for Addiction Medicine, said: ‘We can confidently say that these findings strongly suggest that abstaining from cannabis helps young people learn, while continuing cannabis use may interfere with the learning process.’

Among 88 teenagers and young adults who used cannabis at least once a week, 55 came off it for a month.

After just a week, they performed substantially better on a verbal memory task which involved being shown a list of 18 words twice before being asked to recall them 20 to 30 minutes later.

Improvements in visual memory were not deemed significant, and their ability to concentrate also did not improve, which may be due to the long-term effects of cannabis.

But their improved verbal memory, relative to those who did not stop taking cannabis, suggests the drug may well harm young people’s thinking skills.

Dr Schuster said the ‘good news part of the story’ was that at least some of its effects are not permanent and that they can fade quickly after drug use stops.

The study, published in the Journal of Clinical Psychiatry, found that those who stopped using cannabis saw a dramatic improvement in their ability to retain information after a week. This was judged based on the number of words remembered, and for how long afterwards.

THC, the ingredient in cannabis which produces a ‘high’, has been linked to problems with verbal memory.

More than one in ten Britons aged 18 to 24 – or around one million young people – have used cannabis. Seizures by police have fallen, despite warnings about the drug’s potential links with psychosis.