America is awash in immediate-release (IR) opioids. About 90 percent of all opioid pain medications prescribed – or 160 million prescriptions a year – are for IR formulations like hydrocodone and acetaminophen or oxycodone and acetaminophen combinations. Many people who are currently addicted to opioids became medically addicted. Their first exposure to opioids was from a legal prescription, and for many, that prescription was written for an IR formulation of these drugs. Many addicted patients may then move on to higher dose formulations or more accessible illegal street drugs.
Read more here: https://blogs.fda.gov/fdavoice/index.php/2017/09/fda-takes-important-steps-to-stem-the-tide-of-opioid-misuse-and-abuse/