On the Horizon: The Synthetic Opioid U-49900.

Synthetic opioid use continues to be a problem in the United States. New designer opioids continue to be released as "research chemicals" by vendors, leading to widespread use and potentially devastating consequences. U-49900 is a new synthetic opioid with limited clinical data available. Herein, we provide an overview of U-49900, the anecdotal accounts of U-49900 use that clinicians need to be made aware of, and a call for the federal government to take immediate action in curtailing the use of U-49900.