Nicotine in cigarettes may trigger psychiatric disorders, raising a smoker's risk of committing suicide, a new study has warned.
Previous research has shown that cigarette smokers are more likely to commit suicide than people who don't smoke.
This reality has been attributed to the fact that people with psychiatric disorders, who have higher suicide rates, also tend to smoke.
But researchers at the Washington University School of Medicine in St Louis found that smoking itself may increase suicide risk and that policies to limit smoking reduce suicide rates.
In a study published in the journal Nicotine & Tobacco Research, a team led by Richard A Grucza, reported that suicide rates declined up to 15 per cent, relative to the national average, in US states that implemented higher taxes on cigarettes and stricter policies to limit smoking in public places.
"Our analysis showed that each dollar increase in cigarette taxes was associated with a 10 per cent decrease in suicide risk," said Grucza, associate professor of psychiatry.
"Indoor smoking bans also were associated with risk reductions," he said.
Grucza's team analysed data compiled as individual US states took different approaches to taxing cigarettes and limiting when and where people could smoke.
From 1990 to 2004, US states that adopted aggressive tobacco-control policies saw their suicide rates decrease, compared with the national average.
The opposite was true in states with lower cigarette taxes and more lax policies toward smoking in public.
In those states, suicide rates increased up to 6 per cent, relative to the US national average, during the same time period.
From 1990 to 2004, the average annual suicide rate was about 14 deaths for every 100,000 people.
Using statistical methods, the researchers compared rates of suicide in states with stricter tobacco policies to rates in states with more lenient laws and lower taxes.
They also determined whether people who had committed suicide were likely to have smoked. They learned that suicide risk among people most likely to smoke was associated with policies related to tobacco taxes and smoking restrictions.
Grucza suspects nicotine may be an important influence on suicide risk.
"Nicotine is a plausible candidate for explaining the link between smoking and suicide risk," Grucza said.
"Like any other addicting drug, people start using nicotine to feel good, but eventually they need it to feel normal. And as with other drugs, that chronic use can contribute to depression or