“The science is not there to say ‘one toke for women, two tokes for men,’ as is the case with alcohol and blood levels,” she said. “The science is essentially behind the legislation.”

— At McMaster University in Hamilton, Michael Amlung, a professor of psychiatry who studies addictions, told me that defining impairment isn’t the only outstanding cannabis issue on researchers’ agendas.

“One of the things that’s concerning from my standpoint in terms of research is when we’re talking about cannabis use among youth. We don’t know much about the effects of cannabis on the developing brain — and the brain does continue to develop into the teen years and into the early 20s,” he said. “There is some preliminary evidence that heavy cannabis use during those time periods can impact typical neural development, but we don’t understand yet what the potential long-term consequences may be.”

He is also dismayed about many claims around marijuana, particularly the idea that different strains offer specific properties — like, say, aiding sleep.

“There is a lot of snake oil at this point,” he said. “This idea that cannabis is a miracle plant that will cure all of your ailments is, at least currently, not supported by the science.”

Genetic analysis by botanists, Professor Amlung said, shows that there has been so much cross breeding between strains “that those labels are largely meaningless from a scientific standpoint.”