Comorbidity: Addiction and Other Mental Illnesses mental illnesses Research one or more symptoms of existing mental illness National Institute on Drug Abuse National Institute on Drug Abuse National Institute on Drug Abuse National Institute on Drug Abuse addiction Mental illness and addiction National Institute on Drug Abuse mental health conditions maintains National Institute on Drug Abuse puts it well The stats show National Institute on Drug Abuse mental illness mental illnesses bigger role maintains bigger role connection addiction often co-occurs substance abuse and mental illness co-occurring mental illnesses Mental illness and substance abuse go hand-in-hand common causal factors one or more symptoms of existing mental illness National Institute on Drug Abuse addiction addiction often co-occurs estimates that 40% of people co-occurring disorder one or more symptoms of existing mental illness actually cause 40 percent shared vulnerability one or more symptoms of existing mental illness puts it well National Institute on Drug Abuse treatment for addiction and psychosis maintains directly connected National Institute on Drug Abuse 40 percent Comorbidity: Addiction And Other Mental Illnesses maintains National Institute on Drug Abuse may become worse Comorbidity: Addiction and Other Mental Illnesses