People who smoke cannabis are more likely to suffer from a shrinking vocabulary as they get older, research has found.

The Coronary Artery Risk Development in Young Adults (CARDIA) study followed almost 3,500 men and women over a period of 25 years. A total of 2,852 of the study’s participants admitted to using cannabis in the past but just 392 had carried on using the drug into middle age.

People taking part were asked to complete a number of tests assessing cognitive performance, including remembering words from a list. The researchers found that a history of using cannabis was linked to having a poorer verbal memory, although it did not seem to affect other areas of cognitive function.

The results, which have been published online by JAMA Internal Medicine, showed that the longer people had smoked cannabis for, the fewer words they could remember.

More research needed

Reto Auer, from the University of Lausanne in Switzerland, said: “Future studies with multiple assessments of cognition, brain imaging and other functional outcomes should further explore these associations and their potential clinical and public health implications.

“In the meantime, with recent changes in legislation and the potential for increasing marijuana use in the United States, continuing to warn potential users about the possible harm from exposure to marijuana seems reasonable.”

Cannabis is the most widely used drug in the UK and can cause anxiety, paranoia, panic attacks and even hallucinations. Using it regularly has also been linked with mental illness including schizophrenia.

Employers wanting to crack down on staff using cannabis may consider using workplace testing to make sure productivity and safety is not being affected by substance misuse. It is believed that carrying out random drugs tests can help reduce the risk of accidents in the workplace as it will deter employees from using illegal substances before or during their shifts in case they are asked to take a test.