Drug-overdose deaths have come in roughly three waves. The first wave began with the release of OxyContin and other slow-release prescription opioids in the late 1990s. Starting around 2010 the growing number of people in addiction, a crackdown on prescription opioids, and a greater supply of heroin combined to trigger a second wave of deaths. Around 2013 the third wave hit, fueled by illicit fentanyl and its analogs; within three years it was the deadliest drug in the country. Simultaneously, overdose deaths began increasing for unrelated drugs, such as cocaine and methamphetamine. Experts are still trying to figure out the relationship between these increases.