Altered striatal dopamine signalling is linked to drug abuse; however, the precise nature of any changes in dopamine release in addiction are unclear. The authors here show that phasic dopamine release in the striatum is decreased during the escalation of cocaine self-administration in rats. In the ventromedial striatum, this decrease was correlated with the increased drug taking. Increasing striatal extracellular dopamine levels by administering L-DOPA was able to reverse the escalation of cocaine self-administration. Thus, decreased phasic dopamine release may contribute to the onset of drug abuse.