Psychologists and psychiatrists use the term personality to describe the core characteristics of outlook and behavior that distinguish each human being. An individual\u2019s personality traits can have a major influence on whether he or she gets involved in substance use or develops serious substance problems. In a study published in October 2014 in the journal Drug and Alcohol Dependence, a team of Dutch and American researchers explored the impact that personality has in determining if a consumer of illegal\/illicit opioid substances will go on to develop an opioid addiction. Personality Human beings start to develop their core personality traits at a very early age. As a rule, these traits are somewhat fluid during early childhood and adolescence. However, by the time he or she reaches adulthood, the typical person has a more or less fixed personality that largely determines outlook and behavior for the rest of his or her life. Psychologists commonly identify five core personality traits, sometimes known as the Big Five. These traits are openness, extraversion, agreeableness, conscientiousness and neuroticism. Aspects of openness include imagination and curiosity, while aspects of extraversion include enthusiasm and assertiveness. Aspects of agreeableness include sympathy and generosity, while aspects of conscientiousness include responsibility and reliability. Aspects of neuroticism include self-pity and anxiousness. A personality test called Cloninger\u2019s Temperament and Character Inventory takes another approach. Under the terms of this test, any given person\u2019s typical daily attitude or temperament has four basic components: harm avoidance, novelty seeking, persistence and reward dependence (need for approval). In addition, any given person has three aspects or dimensions of character: cooperativeness, self-directedness and self-transcendence (spiritual orientation). Under the terms of the Big Five approach and the Temperament and Character Inventory, every individual has a mixture of specific traits that form his or her personality. Opioid Addiction Opioid drugs and medications are chemically related substances that travel to the brain after introduction into the bloodstream through such methods as oral ingestion, inhalation and injection. Once inside the brain, opioids do three main things: slow down the brain\u2019s ability to keep its nerve cells actively communicating, reduce pain sensitivity and increase levels of the brain\u2019s main pleasure-producing chemical, dopamine. The pleasure triggered by opioid use is great enough that significant numbers of people establish a pattern of abusive intake by repeatedly consuming an opioid in a method or at a rate not sanctioned by a doctor. At a certain point, an abusive pattern of opioid intake can lead to permanent changes in normal brain chemistry and the onset of a substance-reliant state known as opioid dependence. In turn, people affected by opioid dependence often develop the highly damaging symptoms of opioid addiction. Impact on Addiction Risks In the study published in Drug and Alcohol Dependence, researchers from the University of Amsterdam, the University of Utrecht and several other Dutch institutions, as well as the U.S.\u2019s Rockefeller University, used an examination of 598 adults to explore the impact that personality traits have on the odds that any given illicit\/illegal opioid consumer will develop an opioid addiction. Four hundred two of the study participants had developed such an addiction and were enrolled in treatment; another 161 participants used illicit\/illegal opioids but never developed an addiction. The remaining 135 participants did not use illicit\/illegal opioids and acted as a comparison or control group. The researchers used Cloninger\u2019s Temperament and Character Inventory to identify the personality traits of the members of all three groups. After reviewing the results of the personality testing, the researchers concluded that people who use illicit\/illegal opioids without getting addicted typically have a different mixture of personality traits than people who use these substances and subsequently develop an opioid addiction. Specifically, while opioid abusers who never develop an addiction have traits that may initially encourage involvement in opioid consumption (e.g., a love of novel experiences and a spiritual outlook), they also have personality traits that appear to limit their chances of transitioning into addiction (e.g., a desire to receive approval from others and a relatively strong sense of self-direction). The study\u2019s authors undertook their project, in part, because previous investigations of the impact of personality on opioid addiction usually did not compare the traits of non-addicted opioid abusers to the traits of addicted abusers. Interestingly, they note that non-addicted opioid abusers are more likely to be spiritually oriented than addicted opioid abusers and people who don\u2019t use illicit\/illegal opioids.