Smoking may hike the risk of developing depression and schizophrenia, The Mail Online says citing a study.
Bristol University experts discovered smokers face almost twice the risk of getting the mental health conditions.
The study, conducted on nearly half a million people, adds to the large catalogue of health issues already linked to tobacco.
Academics could not prove smoking causes depression or schizophrenia, warning that they only found more evidence to link them.
Results, published in the journal Psychological Medicine, also showed people with the conditions are more likely to start smoking.
But the evidence to suggest smoking leads to poor mental health - as opposed to the other way round - was much stronger.
Lead author Dr Robyn Wootton and her team believe nicotine hampers dopamine and serotonin receptors in the brain.
Dopamine is a naturally occurring chemical and regulates one's emotions, as does serotonin - known as the 'happy chemical' which contributes to wellbeing.
The scientific paper calls for more to be done to help smokers with mental health conditions to stop.