Many patients with opioid addiction continue to use opioids during and after treatment, and their career of drug taking is usually punctuated by repeated treatment admissions and relapses. Personality traits are considered risk factors for drug use, and, in turn, the psychoactive substances impact individuals' traits. The most widely used system of traits is called the Five-Factor Model (FFM). Studies have shown that persons who use heroin are consistently depicted as high on Neuroticism and higher Extroversion, also they are described as more impulsive and less sociable. Those who maintain abstinence are characterized by a higher Agreeableness and Conscientiousness. Treatment programs for opioid addiction vary substantially in treatment processes, and an early identification of patients traits that address their strengths and weaknesses within specific treatment settings could be useful in decreasing the possibility of relapse.