<p>Despite the unprecedented toll of the opioid epidemic in the United States, the neurobehavioural features of opioid use disorder remain substantially understudied. Impulsivity has a central role in substance use disorders, but might not be as prominent in opioid addiction. Impulsivity has multiple dimensions, related to stability and change (trait versus state) and emotion (emotion elicited versus emotion neutral). In this Review, we suggest that trait and state impulsivity in opioid use disorder is primarily emotion elicited and mediated by negative reinforcement mechanisms that aim to relieve opioid users from acute or protracted opioid withdrawal or chronic negative affective states (for example, physical or emotional pain). Indeed, negative reinforcement mechanisms are involved in all stages of the opioid addiction cycle and are more heavily implicated in opioid use than in other substance use. Moreover, we identify that impulsive behaviour in opioid use disorder frequently occurs in the context of negative affectivity manifested as a personality trait (such as negative urgency) or a personality disorder (such as psychopathy), which are less common in other substance use disorders. Further examination of these mechanisms will deepen current knowledge of the neurobehavioural underpinnings of opioid addiction and improve clinical treatment.</p>