Cocaine, methamphetamine, and heroin generate headlines when it comes to drug use. But in recent years, legal substances have done considerably more damage. Overdose deaths in the United States caused by prescription painkillers, for example, now exceed deaths caused by cocaine and heroin combined. At least those painkillers require a doctor’s note. As Demi Moore’s recent hospitalization for alleged use of nitrous oxide suggests, there is a reason why a growing number of over-the-counter, legal, and quasi-legal substances have public health and law-enforcement officials alarmed. Here are seven of the most dangerous legal drugs.