Canadian experts are telling doctors to think twice before prescribing medicinal marijuana - as the harm may outweigh the benefits for many conditions.
Medicinal marijuana's been legal in Canada since 2001, but the new guidelines there throw a different light on the debate about medical marijuana in New Zealand.
Guidelines to be distributed to 30,000 doctors in Canada suggest "taking a sober second thought" before prescribing.
Researchers say in some cases cannabis performed little better than a placebo for pain relief and alternatives were better.
The debate has intensified in New Zealand since the late trade union leader Helen Kelly openly used medicinal cannabis to ease the pain of her terminal cancer.
Cannabis campaigners say Canada's new guidelines are not surprising because even the writers accept much of the research is biased.
NORML's Chris Fowlie says some opiates and other highly addictive drugs have similar success but powerful side effects.
"This is the result of 90 years of prohibition that has blocked research into the benefits of cannabis while emphasising research about harms," he says.
"Now gabapentin is routinely prescribed and kills thousands of people and has a really high risk of addiction and overdose and the benefits are not that dissimilar.
"So it's interesting that they're pointing to the harms but with the opiates that they already prescribe it seems that those harms are worth the benefits."
Dr Trecia Woulds works with women who use drugs. She says because the evidence isn't clear either way clinical trials are urgently needed.
"We're moving towards evidence-based more and more here in New Zealand," she says.
"We've got good science advisers and it would be helpful if they sort of weighed in on this because I think that's what's going to be critical."
The medical cannabis Bill, which would enable terminally ill people to possess and use cannabis, passed its first reading in the House last month and is now before a select committee.