The scientific evidence for the benefits of medical marijuana is of mixed quality and in some cases lacking altogether, according by researchers at the University of Maastricht.

The researchers looked at 79 trials involving almost 6,500 people and found there is ‘moderate quality’ evidence to suggest medical marijuana relieves chronic pain. But the evidence that cannabinoids relieve the nausea associated with chemotherapy and sleep disorders is of low quality, the researchers said.

The findings are published in the American medical association’s magazine JAMA.

The researchers found that most studies suggest that cannabinoids are associated with improvements in symptoms, but these associations did not reach statistical significance in all studies.

Depression

‘We did not find a single randomised control trial looking at the effect of medical cannabis on depression,’ professor Jos Kleijnen told the Volkskrant. ‘This is odd because doctors do prescribe it for depression. The studies also detail a lot of side effects. The pain might be reduced but you end up dizzy and tired. Is it then worth it?’

Common adverse effects included dizziness, dry mouth, nausea, fatigue, euphoria, vomiting, disorientation, drowsiness, confusion, loss of balance and hallucinations, the research team said.

Kleijnen said the research did not indicate that experiments with medical marijuana should be abandoned. ‘All I am saying is the evidence is thin and the quality of the research needs improving,’ he said.

The Netherlands has some 5,000 official users of medical marijuana but this figure does not include people who grow their own or buy supplies in licenced cafes, the Volkskrant says.