Background:
People with mental illness have higher rates of smoking than the general population and are at greater risk of smoking-related death and disability. In smokers from the general population, electronic cigarettes (e-cigarettes) have been shown to have a similar effect on quit rates as nicotine replacement therapy, but little is known about their effect in smokers with mental illness.

Methods:
Secondary analysis of data from the ASCEND trial involving 657 dependent adult smokers motivated to quit, randomised to 16 mg nicotine e-cigarette, 21 mg nicotine patch, or 0 mg nicotine e-cigarette, with minimal behavioural support. Using self-reported medication use and the Anatomical Therapeutic Chemical Classification System, we identified 86 participants with mental illness and analysed their cessation and smoking reduction outcomes.

Results:
For e-cigarettes alone, and all interventions pooled, there was no statistically significant difference in biochemically verified quit rates at six months between participants with and without mental illness, nor in smoking reduction, adverse events, treatment compliance, or acceptability. Rates of relapse to smoking were higher in participants with mental illness. Among this group, differences between treatments were not statistically significant for cessation (patch 14% [5/35], 16 mg e-cigarette 5% [2/39], 0 mg e-cigarette 0% [0/12], p = 0.245), adverse events or relapse rates. However, e-cigarette users had higher levels of smoking reduction, treatment compliance, and acceptability.

Conclusions:
The use of e-cigarettes for quitting appears to be equally effective, safe, and acceptable for people with and without mental illness. For people with mental illness, e-cigarettes may be as effective and safe as patches, yet more acceptable, and associated with greater smoking reduction.

Trial registration:
Australian New Zealand Clinical trials Registry, number: ACTRN12610000866000.