This paper reviews some major epidemiological studies undertaken in high-income countries during the last 15 years which have reported the prevalence of mental disorders and substance use disorders and their relationship. Comorbidity between mental and substance use disorders is highly prevalent across countries. In general, people with a substance use disorder had higher comorbid rates of mental disorders than vice versa, and people with illicit drug disorders had the highest rates of comorbid mental disorders. There is a strong direct association between the magnitude of comorbidity and the severity of substance use disorders. While causal pathways differ across substances and disorders, there is evidence that alcohol is a casual factor for depression, in some European countries up to 10% of male depression. Policies that reduce the use of substances are likely to reduce the prevalence of mental disorders. Treatment should be available in an integrated fashion for both mental and substance use disorders. There is a need to expand the evidence base on comorbidity, particularly in low-income countries.

Objective To assess the immediate impact of the introduction of minimum unit pricing in Scotland on household alcohol purchases. Design Controlled interrupted time series analysis. Setting Purchase data from Kantar Worldpanel’s household shopping panel for 2015-18. Participants 5325 Scottish households, 54 807 English households as controls, and 10 040 households in northern England to control for potential cross border effects. Interventions Introduction of a minimum price of 50p (€0.55; $0.61) per UK unit (6.25p per gram) for the sale of alcohol in Scotland on 1 May 2018. Main outcome measures Price per gram of alcohol, number of grams of alcohol purchased from off-trade by households, and weekly household expenditure on alcohol. Results The introduction of minimum unit pricing in Scotland was associated with an increase in purchase price of 0.64p per gram of alcohol (95% confidence interval 0.54 to 0.75), a reduction in weekly purchases of 9.5 g of alcohol per adult per household (5.1 to 13.9), and a non-significant increase in weekly expenditure on alcohol per household of 61p (−5 to 127). The increase in purchase price was higher in lower income households and in households that purchased the largest amount of alcohol. The reduction in purchased grams of alcohol was greater in lower income households and only occurred in the top fifth of households by income that purchased the greatest amount of alcohol, where the reduction was 15 g of alcohol per week (6 to 24). Changes in weekly expenditure were not systematically related to household income but increased with increasing household purchases. Conclusions In terms of immediate impact, the introduction of minimum unit pricing appears to have been successful in reducing the amount of alcohol purchased by households in Scotland. The action was targeted, in that reductions of purchased alcohol only occurred in the households that bought the most alcohol.

An 11% improvement in depressive symptoms can be achieved through prevention programmes. Single trial evaluations should ensure high quality of the research design and detailed reporting of results and potential predictors.