为什么戒烟如此困难？ 戒烟, 困难

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Why is it so hard to quit smoking?
　　Why is smoking so difficult to give up? Inhaling a puff of smoke from a cigarette sends nicotine molecules zooming up into the brain within seconds. Then the nicotine grabs hold of receptors on brain cells and releases dopamine, the brain's feel-good chemical, bringing feelings of pleasure and comfort.
　　Besides dopamine, smoking also activates the release of other molecules in the brain that make you feel good, including chemicals called endogenous opioids, according to 2004 research from the University of Michigan.
　　And cigarette companies haven't been making it any easier for people to kick the habit. Over the past decade, companies have made changes to the design and ingredients in cigarettes to make them more alluring to first-time smokers, and more addictive for long-time smokers.
　　These changes include adding ammonia to the tobacco, which converts nicotine into a form that gets to the brain faster, as well as adding holes to cigarette filters that allow people to inhale smoke more deeply into their lungs. Other additions, such as sugar and "moisture enhancers," reduce the dry, burning sensation of smoking, making it a more pleasant experience - especially for new cigarette smokers.
　　When you stop smoking, and your nicotine receptors stop being activated. Essentially, you're not getting as much dopamine as you're used to, which can cause feelings of withdrawal. In fact, a 2002 study in the Journal of Consulting and Clinical Psychology showed that people who had quit cold turkey had lingering feelings of depression and tension 31 days later.