ITI-333 is a drug which has a mixed mechanism of action, acting as an antagonist at the 5-HT<sub>2A</sub>, D<sub>1</sub> and ñ1A receptors, and also as a partial agonist at the ü-opioid receptor. In animal studies it blocked the head-twitch response produced by DOI and also reduced responses to morphine, while also reducing the symptoms produced by naloxone-precipitated withdrawal in opioid habituated mice. It has been developed for potential uses in treatment of opioid withdrawal and opioid use disorder.