Students who smoke cannabis will get lower grades, a study has claimed.

Research published in the journal Psychology of Addictive Behaviors found people who take marijuana at university missed more lectures and tutorials than their non-drug using peers and that their work suffered as a result.

But the academics behind the study said there was no proof that smoking cannabis was the main cause of lower grades, although it did play a part. Other factors included drinking alcohol and abusing other drugs, involvement in extracurricular activities and mental health issues including depression.

Lead researcher Dr Amelia Arria, an associate professor of behavioural and community health at the University of Maryland School of Public Health, said the fact that those who smoke cannabis regularly skip lectures and tutorials could reflect their general attitude.

She said: “We think they may be less engaged in college life and may not be taking advantage of all the opportunities it presents.”

Research examined student habits

The research involved looking at the habits and grades of 1,100 University of Maryland students over a period of eight years, starting from their first year of university.

Just over a third (37%) admitted smoking cannabis at least once in the last 30 days while they were in their first year. The study found that in general the more students smoked the drug, the more often they failed to attend lectures.

And, perhaps unsurprisingly, this led to lower grades and meant they took longer to graduate. The study found that if students increased the amount they smoked, their marks fell further but those who cut down on their drug use started to get better grades again.

Dr Arria said that students often saw smoking cannabis as harmless and benign and that more should be done to raise awareness of the risks.

If smoking cannabis affects academic performance, it could also affect productivity at work. AlphaBiolabs offers workplace drug testing to employers so they can find out whether their staff are abusing substances including cannabis.