A new study finds smokers are two to four times more likely than nonsmokers to commit suicide. State public health interventions such as indoor smoking bans and cigarette taxes could reduce suicide rates by as much as 15 percent, the researchers say.

“It is an open question whether smoking is a direct risk factor for poor mental health outcomes, and by extension, suicide,” the researchers write in the journal Nicotine & Tobacco. “If so, this would have significant implications for public health and clinical practice because it would establish smoking as a common and modifiable risk factor for suicide. In this case, more effective tobacco control policies and other smoking interventions could be promising means for suicide risk mitigation.”

The researchers, from Washington University School of Medicine in St. Louis, looked at data from the National Center for Health Statistics. They found each dollar increase in cigarette taxes could decrease suicide risk by as much as 10 percent, CBS News reports.

The study found states that adopted strict tobacco control policies between 1990 and 2004 experienced a decrease in suicide rates, while states with lower cigarette taxes and fewer no-smoking laws saw a 6 percent rise in suicides.

“Nicotine is a plausible candidate for explaining the link between smoking and suicide risk,” lead author Richard Grucza, PhD, said in a news release. “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 anxiety, and that could help to explain the link to suicide.”