The government of Canada has introduced legislation to allow adults to possess, share and purchase marijuana, while also strengthening penalties for those who give or sell the products to youth.
Besides the hundreds of thousands of people who are expected in Washington, D.C., to cheer the new president on Inauguration Day, thousands more are planning to protest.
The National Academies of Sciences, Engineering and Medicine sorted through 10,000 studies to determine the good and bad health effects of marijuana. Tight drug restrictions impede research, they say.
Author John Hudak says federal law makes it hard to prove the medicinal value of marijuana. "As a Schedule 1 drug, it is very difficult to do research on the plant," he explains.
The state legalized marijuana at the start of 2014 for anyone 21 or older. An increasing rate of Latino and black youths were arrested for violating that age limit, even as the white arrest rate fell.
Blood alcohol levels match well with a person's impairment. But the THC in marijuana doesn't move around the body the same way, so blood tests can miss people who are stoned.
Does legalization of marijuana mean more drivers will have the drug in their system? New data from Washington state says yes, but does that mean pot has caused more accidents? The answer is unclear.