Marijuana is the most-used illegal recreational drug in America, and its use has surged in recent years, especially among young people. It affects several important brain activities, including coordination, short-term memory, and the ability to make decisions; these effects may continue for weeks or months after discontinuing habitual use. It also affects the lungs the way smoking does, increases heart rate and blood pressure, weakens the immune system, and impacts sexual and genetic development. Quitting the habit is hard. Support someone who is trying to quit, and encourage them to find a new group of friends. If you know someone who uses marijuana, show your concern. They might be defensive and distant initially—but they may act later. www.colorado.edu/alcohol/students/marijuana.html.