High impulsivity predicts the transition to compulsive cocaine taking in rats. The study shows that while high reactivity to novelty predicts the initiation of cocaine self-administration, high impulsivity predicts the development of addiction-like behaviors, including persistent or compulsive drug taking despite aversive outcomes. This suggests a shift from impulsivity to compulsivity during the development of addictive behavior. The study used a model of addiction based on individual differences in compulsive cocaine use. Rats were categorized based on three addiction-like criteria: increased motivation to take the drug, inability to refrain from drug-seeking, and maintained drug use despite aversive consequences. Rats meeting all three criteria were considered 'addicted' and represented 15-20% of the population initially exposed to cocaine. High impulsivity (HI) rats showed higher addiction scores than low impulsivity (LI) rats, while high novelty reactivity (HR) rats did not differ from low novelty reactivity (LR) rats. HI rats were more likely to be in the 2-3 criteria groups, whereas HR, LR, and LI rats were mainly in the 0 and 1 criteria groups. Factor analysis revealed that impulsivity and addiction-like behavior are explained by the same factor, indicating an impulsivity/addiction construct. HI rats displayed greater resistance to punishment of the drug taking response than other rats. Correlational analysis showed that impulsivity predicts compulsivity. However, HI rats did not differ from LI, HR, or LR rats in total cocaine intake, suggesting that the development of compulsive cocaine taking is not due to differential exposure to cocaine. The study highlights that high impulsivity is a key behavioral marker for vulnerability to progress to compulsive cocaine use, a hallmark of addiction. These findings support the idea that impulsivity is a critical factor in the development of addiction, and that the transition from controlled to compulsive drug-taking is driven by high impulsivity. The study also emphasizes the importance of pre-existing impulsivity in addicts and provides a basis for investigating the neurobiological mechanisms underlying this transition.High impulsivity predicts the transition to compulsive cocaine taking in rats. The study shows that while high reactivity to novelty predicts the initiation of cocaine self-administration, high impulsivity predicts the development of addiction-like behaviors, including persistent or compulsive drug taking despite aversive outcomes. This suggests a shift from impulsivity to compulsivity during the development of addictive behavior. The study used a model of addiction based on individual differences in compulsive cocaine use. Rats were categorized based on three addiction-like criteria: increased motivation to take the drug, inability to refrain from drug-seeking, and maintained drug use despite aversive consequences. Rats meeting all three criteria were considered 'addicted' and represented 15-20% of the population initially exposed to cocaine. High impulsivity (HI) rats showed higher addiction scores than low impulsivity (LI) rats, while high novelty reactivity (HR) rats did not differ from low novelty reactivity (LR) rats. HI rats were more likely to be in the 2-3 criteria groups, whereas HR, LR, and LI rats were mainly in the 0 and 1 criteria groups. Factor analysis revealed that impulsivity and addiction-like behavior are explained by the same factor, indicating an impulsivity/addiction construct. HI rats displayed greater resistance to punishment of the drug taking response than other rats. Correlational analysis showed that impulsivity predicts compulsivity. However, HI rats did not differ from LI, HR, or LR rats in total cocaine intake, suggesting that the development of compulsive cocaine taking is not due to differential exposure to cocaine. The study highlights that high impulsivity is a key behavioral marker for vulnerability to progress to compulsive cocaine use, a hallmark of addiction. These findings support the idea that impulsivity is a critical factor in the development of addiction, and that the transition from controlled to compulsive drug-taking is driven by high impulsivity. The study also emphasizes the importance of pre-existing impulsivity in addicts and provides a basis for investigating the neurobiological mechanisms underlying this transition.