Is there a causal effect of smoking on mental health?

This report by academics at the University of Bristol summarises evidence around two key questions about smoking and mentalhealth: 1) does smoking increase the risk of subsequent mental health problems, and 2) does quitting smoking improve mental health symptoms. Establishing whether or not these are true causal effects will help to better target successful public health policies and to hopefully increase life expectancy and improve health amongst individuals with mental illness.

Key messages

• There is a large body of longitudinal research that finds strong evidence for a prospective association between smoking and mental health, this focuses on depression, anxiety and schizophrenia.
• Much of the evidence from Mendelian randomisation studies suggests that smoking behaviours have a detrimental causal effect on mental health. However, there is a high degree of bidirectionality in these relationships.
• However, evidence from discordant twin studies and negative control studies indicates that smoking and mental health share underlying genetic liability which could be biasing results.
• Smoking cessation interventions for individuals with mental illness do not worsen mental health symptoms and may improve them in the long term.

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