Cannabis link to brain inflammation nothing to be alarmed about - expert

New research linking chronic cannabis use with brain inflammation is nothing to get paranoid about, according to a Kiwi expert.

Scientists in Canada and Australia compared 24 young heavy smokers with 27 non-users, and found the former had "higher levels of inflammatory markers in the blood". 

"The long-term cannabis users had higher levels of the brain protein known as a translocator protein," they said in a statement on Thursday.

"Higher levels of this protein were linked with stress and anxiety and also with higher levels of an inflammatory marker in the blood of cannabis users."

Considering many cannabis users smoke the drug to relax, the results were surprising. 

"Having a hypothesis disproven this clearly is rare, but this is a strong finding," senior author Romina Mizrahi of the University of Toronto.

But scientist Suresh Muthukumaraswamy of the University of Auckland's Centre for Brain Research told The AM Show on Thursday he "wasn't particularly alarmed, to be honest".

"This is just what we call an observational study - you take one group, take another group," he explained. "What you can't do based on that is say that cannabis has caused these people to have more inflammation. It could be something else - it could be they have more stress in life. You just don't know. It's not the type of study that allows you to make that kind of inference."

Suresh Muthukumaraswamy
Suresh Muthukumaraswamy. Photo credit: The AM Show

Dr Mizrahi agreed, telling CTV News more research is planned to see if there is a causal relationship between chronic cannabis use and inflammation.

New Zealand next year will hold a referendum on recreational cannabis use. Dr Muthukumaraswamy said opponents of legalisation should think twice before using Mizrahi's study as proof it should stay illegal.

"I don't think you could really make any kind of political inferences in terms of policy, because on the flipside you could potentially argue that a regulated system might actually reduce that kind of harm."

Cannabis users presently have to buy it on the black market where there are no rules or regulations in place in terms of THC and CBD levels. The former is psychoactive, the latter used in medicine. 

"If whatever the Government came up with was regulating and taxing levels appropriately so that high levels of THC weren't appropriate and high levels of CBD were available in the product, that could potentially mean the 400,000 New Zealanders that are taking cannabis every year actually have a safer thing they are using," said Dr Muthukumaraswamy.

"That would actually have net health benefits."

The referendum will take place alongside the 2020 election.