Dr. Yuan studies the mechanisms of opioid actions, especially the antagonism of opioid side effects. He performed clinical development of methylnaltrexe, a novel compound subsequently approved by the FDA for opioid-induced constipation in advanced illness patients. The FDA approved the methylnaltrexe for the treatment of opioid-induced constipation in patients with chronic non-cancer pain in 2014, and its oral tablets in 2016. This new drug now has been approved for use in over 60 countries worldwide. Dr. Yuan also has a specific interest in herbal medicine research, and serves as the Editor-in-Chief of the American Journal of Chinese Medicine. One of his research interests is to investigate the role of the enteric microbiome in cancer prevention and human health in relation to dietary supplement consumption.