A recent study has found there may be a major side effect to smoking marijuana : Impairment while driving. Researchers from AAA found that people who drank alcohol and then smoked marijuana were more likely to commit violations such as running red lights, speeding and distracted driving. Read on— and to ensure your health and the health of others, don't miss these Sure Signs You Have "Long" COVID and May Not Even Know It . 1 The Cannabis and Alcohol Combo Can Lead To People "Driving Distracted," Study Finds "If you choose to use cannabis and use alcohol, generally you tend to be the type of person who takes more risk while driving, like running red lights, speeding, and driving distracted," said Skylar McKinley, Regional Director of Public Affairs for AAA Colorado. That's what KRDO-TV in Colorado Springs, Colorado, reported. According to the Colorado Department of Transportation and Mothers Against Drunk Driving, in 2019 there were 49