Many students spend their university days in a haze of marijuana smoke.

Now, a study has found it affects their grades as well as their health.

Students who smoked marijuana skipped more lectures and tutorials - and the more frequent their marijuana use, the more their studies suffered.

Unsurprisingly, those who failed to turn up to lectures, in turn, had lower grades on average and graduated later than those who attended.

Researchers said students, parents, universities and policymakers should be made aware of the link between taking the drug and missing work.

Students who smoke marijuana tend to skip more lectures and tutorials, leading to lower grades and delayed graduation, a study has found (file photo)

However, they said the findings do not prove that marijuana use was the root cause of students' academic struggles.

The research was published in the journal Psychology of Addictive Behaviors.

Lead researcher Amelia Arria said the study accounted for other factors which affect grades, HealthDay news reports.

These included students' drinking and other drug use, involvement in sports and other extracurricular activities and psychological factors such as depression.

They also measured some personality traits, like the tendency to act impulsively to seek 'sensation.

Dr Amelia Arria, an associate professor of behavioral and community health at the University of Maryland School of Public Health, said the skipping of lectures and tutorials is an 'important finding'.

Besides the obvious effect it would have on grades, it may reflect a broader attitude among college students who regularly smoke cannabis.

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

The team followed 1,100 University of Maryland students for eight years, starting from their first year of university.

PROOF STRONG CANNABIS DOES HARM YOUR BRAIN Smoking super-strength cannabis can cause significant levels of brain damage, a study found. Researchers discovered people who regularly took strong ‘skunk’ cannabis had signs of greater damage to the biggest ‘tract’ of white matter. This area – the corpus callosum – carries signals between the brain’s left and right sides. Damage to it can lead to mental illnesses and psychotic symptoms such as hallucinations, as well as slowing down the brain’s activity. The researchers say their findings demonstrate an ‘urgent need’ to educate the public, medical staff and policy makers about the risks of skunk – the most popular type of cannabis in the UK. Advertisement

In the first, or freshman year, 37 per cent said they had smoked marijuana at least once in the past 30 days, with the average being six days of the month.

In general, the more often they smoked the drug, the more often they skipped lectures.

This tended to translate into lower average grades and a longer time to graduate.

Over time, if students decreased their cannabis use, their grades tended to rebound.

But when smoking increased, their marks tended to drop.

Dr Arria said the findings suggest that college academic help centers should be aware that there is a connection between marijuana use and student performance.

'When students go to an academic assistance office, rarely does anyone ask them about alcohol or drug use,' she said.

Simply asking students about it might be enough to raise their awareness.

She continued: 'Students often see marijuana as benign. But if you ask them questions like, "How often are you smoking marijuana, drinking, partying?" that alone may help them be more self-reflective and make better choices.'

She said policymakers might want consider the academic consequences when deciding whether to make marijuana more available.

However, Paul Armentano, deputy director of the nonprofit organization NORML, which advocates legal marijuana use, said it is impossible to pin the missed classes on cannabis, specifically.

If students decreased their cannabis use, their grades tended to rebound, researchers found (file photo)

'Correlation is not causation, and it would not appear that there is anything unique to cannabis that would cause those who experiment with it to skip classes,' he said.

Instead, he said, it is more likely that other traits - a student's tendency to 'rebel' or act against 'authority,' for instance - are at work.

He did concede society should ideally 'encourage young people to make healthy lifestyle choices, which includes mitigating their use of intoxicants and being able to discern between use and abuse.'

He added: 'These findings reinforce the need for sensible cannabis regulations that seek to better discourage the use of cannabis and the ready access of cannabis by young people,' he said.