Smoking marijuana every day can increase a person's chances of developing coronary artery disease, researchers have determined. In a study led by Stanford University's Dr. Ishan Paranipe, researchers found daily use increases the risk of CAD by one third, compared to people who don't smoke weed at all. “A growing body of evidence suggests that cannabis is not entirely without harm and may actually cause cardiovascular disease,” Paranjpe says. “Thus, the decision to use cannabis must be carefully weighed against the potential for serious heart disease.” Why do people do things they know are bad for them?