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"Giving up smoking is the easiest thing in the world. I know because I've done it hundreds of times." —Mark Twain.

Why do people have so much trouble quitting smoking?

It's certainly common knowledge that cigarette use is one the greatest known health risks. In fact, statistics indicate that the number of deaths linked to cigarette use each year is greater than deaths from HIV, illegal drug and use, motor vehicle accidents, and violent deaths combined. Along with increasing the risk of most cancers, heart disease, diabetes, and a whole host of other serious illnesses, tobacco use is also linked to reduced fertility, poorer health overall, greater absenteeism from work, and greater health care costs.

Despite these health facts being widely known, there is one more detail about tobacco use that needs to be considered: It is highly addictive. According to World Health Organization statistics, there are more than a billion smokers worldwide (including around 16 percent of all Americans). On average, 75 percent of all smokers report wanting to quit at some point, though the overwhelming majority end up relapsing eventually.

In trying to understand what makes tobacco so addictive, researchers have explored the effect that nicotine and other chemical ingredients found in tobacco can have on the human brain. Certainly there is evidence suggesting that chronic tobacco use can lead to physical dependence and withdrawal effects similar to what occurs with other psychoactive substances.

But is this enough to explain why people are so prone to relapsing? A new meta-analysis published in the journal Experimental and Clinical Psychology argues that it isn't. Written by Lea M. Martin and Michael A. Sayette of the University of Pittsburgh, their research examines the role that social factors can play in smoking and what this can mean for people trying to quit.

As Martin and Sayette point out in their review, isn't enough by itself to explain why smokers have trouble quitting. Even though nicotine replacement therapy is widely available, the actual success rate for helping people quit smoking has been modest at best. Also, casual smokers often have as much trouble quitting as chronic smokers — even though they aren't taking in the level of nicotine needed to produce withdrawal effects.

In recent years, researchers have been taking a closer look at the emotional and social aspects of tobacco use and how they can reinforce the need to smoke for many people. For example, studies show that smoking is much more common in people who are facing social difficulties or are otherwise disadvantaged by society. This includes people suffering from different kinds of mental illness, who are twice as likely to smoke compared to people without mental illness.

Smoking is also extremely common in prison populations where cigarettes and tobacco have become an informal currency exchanged between inmates. Smoking is also much more frequent in minority populations (including racial and sexual minorities), as well as among people with lower levels of and socioeconomic status. Many of these same disadvantaged groups also show significantly higher health care needs, as well as being less likely to succeed at quitting than the general population.

Another factor that has been largely neglected by researchers up to now is the role that smoking plays while socializing. According to one 2009 study, at least one-third of all cigarettes smoked are smoked by people in social situations, and many smokers, when seeing other people smoking, are more likely to smoke themselves. Even when comparing frequent smokers to those who only smoke occasionally, this pattern still holds up.

In recent surveys from the United Kingdom, smokers often view socializing as one of their main reasons for smoking, something that is especially true for smokers under the age of 35. Even "social smokers," who might not otherwise smoke on their own, often do so at parties as a way of blending in with the crowd.

Though this link between smoking and socializing has interesting parallels with other addictive substances, such as alcohol and , it still isn't clear why such a link exists. This brings us to the possible role that nicotine dependence and withdrawal can play in social functioning. In their meta-analysis, Martin and Sayette examined 13 experimental studies testing nicotine use in different populations, including non-smokers, to determine how nicotine exposure influenced social behavior. The studies used a range of different methods to administer nicotine to participants, including the use of tobacco, nicotine gum, nasal sprays, and nicotine patches. Social functioning was measured by the ability to pick up nonverbal social cues, such as facial expressions, using in-person and computer-based interactions.

Based on their results, Martin and Sayette found strong evidence that nicotine use helps boost social functioning. Not only did study participants describe themselves as being friendlier, more , and less socially after ingesting nicotine, but nicotine use helped improve awareness of social and facial cues compared to participants who had abstained from nicotine use for 24 hours or longer. Some of the studies also showed that people suffering from experienced greater problems with social functioning compared to non-users.

What these results suggest is that people who might otherwise experience significant difficulty socializing, whether due to emotional problems or other factors, may be more likely to rely on tobacco as a way of overcoming . This also helps explain why quitting smoking can be so difficult for many people, who see it as necessary in interacting with others.

Also, since smokers are more likely to socialize with other smokers, trying to quit smoking will also mean back on social settings in which tobacco is widely used and, as a result, becoming much more isolated while developing new friendships and social networks in which tobacco isn't used. All of which can make problems such as nicotine withdrawal much more difficult to overcome, since many people may not be prepared to handle what this can mean for their social functioning, at least in the short run.

Though more research is needed, these studies highlight the role that nicotine use and nicotine withdrawal can play in the social lives of smokers. Though most smokers try to quit at some point, this link between nicotine use and social functioning helps explain why relapsing continues to be so common. While this link has been largely overlooked up to now, recognizing how social context can reinforce nicotine use may provide a better understanding of why smoking can be so addictive. And, in time, it may pave the way for more effective methods to help smokers quit for good.