It has previously been shown that there is a relationship between age of first intoxication (AFI) and mental health disorders. However, many studies in this area tend to focus on the relationship between the AFI and substance-use disorder, rather than other mental illnesses, or how pre-existing mental disorders predict substance-use in teenagers. Burke et al (1990) found that the hazard rate for developing a substance-use disorder is highest when the AFI is between ages 15 and 19 and found that this risk decreases as the individual ages, which is consistent with other literature. This suggests that teenage years are a vulnerable period for individuals as there is a high potential for the development and maintenance of a substance-use disorder. The impact of pre-existing mental health issues on substance use is demonstrated in a study conducted by Sung et al (2004), which found that girls who struggle with anxiety before the age of 16 have an increased risk of substance-use disorder, and boys with a history of depression in childhood and early adolescence also have an increased risk. Research suggested that substance-use disorders can also be a symptom of mental illnesses, for example, Robins et al (1985) found evidence that implies this disorder is a symptom of antisocial personality disorder. However, there is a lack of investigation into whether the AFI is associated with the onset of psychopathological symptoms.