Canada just legalized marijuana. That has big implications for US drug policy.

Marijuana smoke lingers in front of Parliament Hill during a 4/20 rally in Ottawa, Ontario, Canada

Canada, like the US, is part of international drug treaties that explicitly ban legalizing marijuana. Although activists have been pushing to change these treaties for years, they have failed so far — and that means Canada will be, in effect, in violation of international law in moving to legalize.