Research on alcohol use in individuals with diabetes is limited. Major depressive disorder (MDD), bipolar disorder (BD) and generalized anxiety disorder (GAD) are often comorbid with diabetes. Furthermore, heavy drinking is more common in individuals with these mental disorders compared to the general population. Therefore, individuals with comorbid diabetes and a mental disorder may be at an increased risk of heavy drinking, but little is known about alcohol use in these populations. The present study tested the hypothesis that individuals with comorbid diabetes and MDD, BD or GAD would be more likely to drink heavily compared to individuals without diabetes or a mental disorder. Data were collected in the cross-sectional 2012 Canadian Community Health Survey-Mental Health (CCHS-MH), and 14,302 adults, 1698 of whom had diabetes, participated. ANOVAs were used to examine main effects of diabetes, each mental disorder and their interactions on alcohol quantity (drinks per day) and frequency (drinking occasions per week/month). Results showed that there was a significant interaction between diabetes and MDD on alcohol quantity, such that those with both diabetes and MDD consumed less drinks compared to those with MDD only or neither MDD nor diabetes. There was no significant difference between those with diabetes only or both diabetes and MDD. The same interaction was observed for diabetes and BD on alcohol quantity. This study suggests that contrary to the hypothesis, among individuals with diabetes, having a mental disorder does not increase the risk of heavy drinking.