Addiction to opiates has increased in recent years. This resurgence in its consumption shows the need to continue to investigate the role of personality in addictive behavior. Variables such as self-efficacy are quite helpful in the treatment of drug addicts. The purpose of this study was to examine and quantify the predictive capacity of self-efficacy in treatment groups (Methadone, Cognitive-Behavioral, Alcohol) and a Control group and in the severity of the substance abuse (quantity and chronicity of use). The sample was composed of 181 participants (97 men and 84 women), who were divided into 4 groups: Methadone, Cognitive-behavioral, Alcohol and Control. Their self-efficacy was measured using the Self-efficacy scale (SE) and the Addictive Behavior Research Interview (EICA). The results showed the self-efficacy is inversely related to the Methadone, Cognitive-behavioral and Alcohol groups and directly related to the Control group. Regarding the severity of the drug use, we found that self-efficacy was inversely related to the quantity of drugs consumed and directly related to chronicity. The study proposes the need to evaluate self-efficacy along with other personality measures, as it is not enough to believe that one is capable of successfully doing something (self-efficacy), but it is also important to show it (coping).