On the rise for more than 15 years, poisoning is now the second leading cause of unintentional injury death in the United States. Unintentional poisoning has surpassed motor vehicle crashes as the leading cause of unintentional injury death among people 35. In a new study, researchers found that hospitalizations for poisoning by prescription opioids, sedatives and tranquilizers in the US have increased by 65 percent from 1999 to 2006.