Significant numbers of people diagnosed with serious mental illness also have co-existing problems with substance use disorder (substance abuse and\/or substance addiction). Evidence shows that the simultaneous presence of these two problems increases the odds for aggressive or violent behavior. In a study published in July 2014 in the Journal of Substance Abuse Treatment, researchers from three U.S. institutions looked at what happens to the aggression levels of mentally ill people who receive treatment for their substance problems. These researchers concluded that a successful reduction of substance intake can lead to reduced aggression levels in affected individuals. \r\nSubstance Use and Mental Illness\r\nMental health guidelines in the U.S. classify substance use disorder as a form of mental illness. When a person affected by substance abuse or substance addiction also has impairing symptoms of a separate, serious mental illness, experts in the field refer to the resulting combination of symptoms as a dual diagnosis. Specific mental illnesses found in people with such a diagnosis include schizophrenia, major depression and bipolar disorder. Apart from any substance-related concerns, these illnesses commonly produce serious or severe disruptions in the ability to maintain a sufficient level of psychological health and well-being. Several partially overlapping factors help explain simultaneous problems with severe mental illness and substance use. First, a mentally ill person who doesn\u2019t receive effective treatment has an increased chance of using drugs or alcohol as part of an unsupervised attempt at self-medication. A person affected by mental illness may also experience a substantial worsening of his or her symptoms while under the influence of drugs or alcohol. In addition, some people develop symptoms of severe mental illness for the first time after establishing a damaging pattern of substance use.\r\nDual Diagnosis and Aggression\r\nMany people consciously or unconsciously believe that individuals dealing with the effects of mental illness are more violent than the rest of the adult population. However, the linchpin in aggressive or violent behavior may be the combined presence of mental illness and substance abuse\/addiction. According to the results of a project conducted in the first decade of the 2000s called the MacArthur Violence Risk Assessment Study, people with a dual diagnosis are over 50 percent more likely to commit violent acts than people who only have problems related to a serious mental illness. The authors of this study attributed the increased risks for violence\/aggression to the added impact of substance use. In people affected only by mental illness, some of the risk for violent or aggressive behavior may come from genetic factors not related to the presence of diagnosable mental health problems.\r\nImpact of Substance Treatment\r\nIn the study published in the Journal of Substance Abuse Treatment, researchers from St. John\u2019s University, the State University of New York at Buffalo and Syracuse University used a six-month examination of 278 adults to assess what happens to the aggression levels of mentally ill people who receive treatment for their substance problems. All of these adults qualified for a dual diagnosis and were receiving treatment in an outpatient program designed for people with such a diagnosis. In addition to analyzing the behavioral changes in study participants who successfully lowered their substance intake, the researchers sought to determine if substance use or severe mental illness plays the critical role in aggressive\/violent conduct. After completing their assessment, the researchers concluded that dual diagnosis treatment does lead to a significant decline in violent\/aggressive behavior. When they explored this finding further, they concluded that the benefit is related to increased involvement in the treatment process. In turn, they attributed increased involvement to lowered intake of drugs and\/or alcohol. Based on this conclusion, they identified substance use as the key factor in the relationship between substance use, severe mental illness and acts of aggression or violence. Interestingly, the researchers found that severity of mental illness at the onset of treatment does not consistently help determine which people with a dual diagnosis will act in an aggressive or violent manner. Overall, they concluded that substance treatment provides two benefits for dual diagnosis patients. First, it leads to reduced exposure to substance-related harm. It also decreases the odds that a person affected by a dual diagnosis will act violently at some later point during or after the treatment process.