There is a profound co-occurrence of substance abuse and mental illness. Both addiction and mental illness have life-altering effects on those affected. Excessive drug use undoubtedly damages the body. Addiction and side effects of drugs (such as hallucinations and paranoia) place a strain on psychological health, while social conditions often deteriorate as the need for drug use outweighs the need to maintain relationships . Similarly, people suffering from a mental health crisis not only experience psychological symptoms, but many have their physical health affected (i.e. loss of appetite, trouble sleeping), as well as their position in society due to anxiety or stigma attached to the disease. Subsequently, this student asked the question: Does mental illness lead to addictive behaviors, or is it the heavy use of addictive drugs that leads to mental health problems? This essay will first define addiction, then explore both sides of the debate and finally suggest how these issues can be addressed in Ireland. The addictive substances examined will be alcohol and cannabis, while the main psychological conditions will be depression, schizophrenia and bipolarity. To complement this student's degree, the focus will be on adolescents throughout this essay. Drug addiction is a significant problem across the world; Compton et al. (2007) found that 7–10% of people will experience either abuse or dependence on illicit drugs during their lifetime. Addiction has been defined by the American Psychological Association (2014) as a condition in which the body must take a drug to avoid physical and psychological withdrawal symptoms. Westreich (2009) argues that this is not simply a pathological point...... middle of paper ...... health promotion in Ireland; especially as studies have shown that Irish teenagers suffer from more mental disorders than their peers in other countries. This trial investigated whether mental illness was a trigger for the use of addictive substances or whether excessive use of these substances led to poor mental health. A detailed argument was presented focusing on cannabis and alcohol addiction. It concludes that there is a link between addiction and mental illness, and that both can be considered a risk factor for the other. The focus throughout the essay was on adolescence, with the teenage years proving most vulnerable to both mental illness and substance abuse. This student believes resources need to be invested in promoting positive mental health among Irish adolescents to reduce the risk of future addictive behaviors in the next generation..