A new study has found that frustration could be an additional factor in substance use disorders. The findings of the study were published in the journal 'Psychopharmacology'. A team from The University of Texas Medical Branch at Galveston (UTMB), which focused on drug addiction research, has pioneered a new way to study frustration as a factor in substance use disorders. Traditional addiction research has focused on three aspects of substance use disorders: craving, impulsivity, or habit. Scientists hypothesized that a fourth factor, frustration, could also lead to an escalation of drug use and addiction. The study noted that research into the role of frustration and substance use disorders is sparse, but a number of studies suggest that persons with substance use disorders have lower frustration tolerance. Studies have shown that sensitivity to frustration correlates with relapse among those with substance use disorders. The UTMB studies used a rat model to focus on frustration-related behaviour. Rats can be trained to press a lever for food or drugs (reinforcers), and frustration is defined as when a subject is unable to achieve a reinforcer, receives less of a reinforcer than anticipated, or has to work harder to achieve a reinforcer.