Another danger can be added to a list tobacco-driven dangers that include various cancers, pulmonary disease, and cardiovascular disease: suicide. A new study has found that interventions such as cigarette excise taxes and smoke-free air policies have a surprising — and welcome — side benefit: reducing the risk of suicide among those most likely to smoke.

Smokers have a higher risk for suicide, and for a long time it was believed the risk was associated with the psychiatric disorders that can affect many smokers. However, the results of the current study suggest that smoking itself may increase the risk for psychiatric disorders, or make them worse, which can raise the risk of suicide.

Instead of smoking to feel good, people start to need cigarettes to feel normal; their baseline mood decreases, maybe down to a three, and when they smoke, it increases to a five.

The risk of suicide among non smokers, or people not likely ever to become smokers, shouldn't be influenced by tobacco policies, Richard Grucza, an associate professor of psychiatry at Washington University of Medicine in St. Louis, told TheDoctor. “So the fact that we saw this influence among people who likely were smokers provides additional support for our idea that smoking itself is linked to suicide, rather than some other factor related to policy.”

Grucza and his team analyzed data that accumulated as individual states took different approaches to taxing cigarettes and limiting when and where people could smoke. They found that, from 1990 to 2004, states that adopted aggressive tobacco control policies had a decrease in suicide rates, compared with the national average.

The analysis showed that each dollar increase in cigarette taxes was associated with a 10 percent decrease in suicide risk, Grucza said. But in states with lower cigarette taxes and more lax policies toward smoking in public, suicide rates increased up to six percent.

But how does smoking in and of itself increase the risk of suicide? One contemporary theory of addiction has to do with how the brain changes on chronic exposure to an addictive substance, in this case nicotine, Grucza explained.

Take for example people who, on a scale of one to 10, might have an average daily mood of five. Under the influence of nicotine, a known mood booster, their mood might increase to a seven. But nicotine, like all drugs, tends to create the opposite effect as it leaves the body, so their mood plummets, maybe to a three.

Over time, going through that cycle over and over again, it is thought that their baseline mood state decreases, Grucza said. Instead of smoking to feel good, people start to need cigarettes to feel normal; their baseline mood decreases, maybe down to a three, and when they smoke, it increases to a five.

This is how chronic nicotine exposure can bring on a chronic low, or depressed, mood, said Grucza. “…[T]he brain can adapt to the presence of nicotine in a way that could cause mood and mental health problems.” It is particularly important for those with psychiatric disorders not to smoke.

The take-home message, said Grucza, is simple: don’t smoke, or quit smoking if you are already hooked. And don't think that cigarettes are cheering you up; their long-term effect is quite the opposite.

Many people are starting to use electronic cigarettes, which are much safer in terms of physical health, but they still have nicotine, which can bring on depression. Researchers need to understand more about nicotine itself, according to Grucza.

“So if nicotine is the driving force, and there is good reason to suspect that it is, then nicotine is not the benign substance that everyone thinks it is.”

Many people think nicotine is as safe as caffeine, but Grucza doesn’t think that’s the case. “It's more addictive, and if it's more addictive, then it could really have adverse psychiatric effects.”

The study is published online recently in Nicotine & Tobacco Research.