Cannabis not made safer by increasing CBD content, study finds

Increasing the amount of cannabidiol (CBD) in cannabis does not reduce the negative effects or make it safer, a new study has found.

Kings College London researchers set out to investigate the common belief that ingesting cannabis with higher levels of CBD can protect the user from psychotic experiences and memory loss problems. However, the scientists found no evidence to support that.

Researchers used a set amount of THC - the main psychoactive compound in cannabis - and different dosages of CBD to explore the effect of the oil on cognitive performance or how pleasurable the drug experience was.

The team enlisted 46 healthy volunteers to complete a randomised double-blind trial over four experiments. Each participant inhaled cannabis vapour containing 10mg of THC and different levels of CBD, 0mg, 10mg, 20mg and 30mg.

The participants then completed a series of tasks, questionnaires and interviews designed to measure the effect on their cognitive abilities, the severity of psychotic symptoms, and how pleasurable the drug was.

Overall, the study found increasing the dose of CBD did not significantly change the effects of THC on the three categories above.

The study’s senior author professor Philip McGuire said: “Our data suggest that, at the doses that are typically present in cannabis, it does not protect against the negative effects of THC.

“This challenges the commonly held view by many cannabis users that cannabis with a higher CBD content provides a buffer against the adverse effects of cannabis.”

Lead author of the study, Dr Amir Englund said: “None of the CBD levels studied protected our volunteers from the acute negative effects of cannabis.

“The only effect of CBD we saw was that as the concentration of CBD increased, the more the participants coughed.

“We asked volunteers to listen to a favourite song on each visit and taste a piece of chocolate. Although cannabis increased the pleasurability of music and chocolate compared to when volunteers were sober, CBD had no impact.”

This study was funded by a research grant from the Medical Research Council and has been published in the journal Neuropsychopharmacology.