How do you answer this question at the U.S. border?

It's a simple question, but the answer you provide could get you banned from entering the U.S. for life. Have you ever done drugs? If you answer yes, you're sent back the other way and told to not come back. If you answer no, you better be telling the truth. What's the right way to respond to this question? What happens when pot becomes legal in Canada in October? And what about people, like our own prime minister, who have publicly admitted to using drugs in the past? Reporter Perrin Grauer (The Star Vancouver) takes us through the frustrating inconsistencies of this law, and shares some advice in case you ever find yourself put on the spot.