A dietary supplement — NAC — is showing promise in helping pot addicts overcome the urge to smoke. When it comes to substance use disorders, alcohol use takes the greatest toll, both in dollars and health problems. But marijuana addiction is a growing concern, for a couple of reasons. There may be more users. Pot is now legal in three American states and Canada’s new Liberal government plans to legalize and regulate it. And the level of THC, the active ingredient in marijuana, is now so high, experts worry pot smoking will have worse consequences in the future, especially for...