Finally, scientists can answer the question everyone who has ever gotten too high has been dying to know: 'how long will this last?'
It's still a range, but University of Alberta researchers discovered that cannabis still impairs learning up to 24 hours after consumption - but the effects dissipate fully by the third day.
The team tested how long cannabis would change their study participants' ability to learn new information.
Much remains to be studied, but their research provides a starting point for the Canadian government to establish safety guidelines, now that the country has legalized marijuana.
Smoking, eating or vaping marijuana impairs memory and learning up to 24 hours after consumption, a new Canadian study reveals, two days after weed was legalized there (file)
Canada has been hard at work preparing for nationwide cannabis legalization.
Lead study author, Dr Scot Purdon says that for the last year, Canada has had its watchful eye on US states like Colorado, California and Washington, learning from their successes (and mistakes).
But marijuana's cognitive effects are more complicated and subtle than those from alcohol, and we don't yet have a particularly good way to test.
Dr Purdon has made it his mission to work out what weed does to the brain - and for how long.
We know that cannabis can 'have very significant psychological and cognitive effects,' he told Daily Mail online.
These effects are particularly obvious in the memory, learning and verbal abilities of someone who has recently used cannabis.
So Dr Purdon and his team decided to test these abilities in 120 young people who were frequent users.
He an his team administered the students verbal learning and fluency standardized tests and before and after they used marijuana.
Unsurprisingly, the subjects struggled on these tests in the hours immediately following their cannabis consumption.
But even 48 later, people may still make mistakes they wouldn't have sober.
By 72 hours after cannabis consumption though, people should well back to their baseline, Dr Purdon said, leading him to suggest this could be a good time limit standard for people to return to jobs.
Of course, everyone metabolizes marijuana somewhat differently, and heavy users may even have signs of marijuana in their urine after 28 days.
Dr Purdon also says that his research also clarifies some common notions about marijuana, such as the idea that it makes people more focused.
'A lot of people tell us it's a positive thing [for concentration], but the data don't always bear that out,' he says.
'Its complicated, in that [high] people don't have the distractability that might be necessary in day-to-day functioning. You get so focused on A that you don't notice B, C and D around you.'
And focused or not, his research subjects simply didn't retain or recall information as well within the first couple of days after using cannabis, which is especially pertinent to students who be tempted to light up a joint as a study aid or study break.
Though his research did not examine how long after smoking, eating or vaping weed people were capable of driving cars, it could become important to Canada's laws surrounding road safety and marijuana.
In 2016, marijuana was involved in more fatal car accidents in the US than alcohol was, sparking calls from officials for better testing and stricter laws.
Dr Purdon says that Canada's broad legalization of marijuana is an 'experiment on 33 million people,' and hopes that, now that it's a legal substance, there will be more control over its potency, and greater clarity about how high high is too high - and for how long.