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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.
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為什么戒煙如此困難？吸一口煙可將尼古丁在幾秒鐘內送入大腦。隨后尼古丁將控制腦細胞受體并釋放出多巴胺——大腦中感覺良好的化學成分，能給人帶來愉悅和舒適的感覺。
密歇根大學2004年的一份研究表明，除了多巴胺，吸煙還能激發大腦中使人感覺良好的其他化學分子的釋放，包括被稱為內源性類鴉片活性肽的化學分子。
此外，煙草公司的“努力”也致使人們更難戒掉這個習慣。在過去10年，煙草公司改變了香煙的設計和成分，使它們對第一次吸煙的人更有吸引力，使長期吸煙的人更容易上癮。
這些改變如，在煙草中加入氨，它將尼古丁轉變為一種可更快進入大腦的分子形式，并增加了煙嘴中的孔，這使人們能將煙霧更深度地吸入肺部。其他的添加成分如，糖和水分保持劑，這樣就減少了吸煙時的干燥和焦灼感，使吸煙成為更愉悅的經歷——尤其是對新煙民而言。
停止吸煙后，你尼古丁受體不再被激發，因而你無法得到你習慣得到的那么多多巴胺。這會引起退縮的感覺。實際上，《咨詢與臨床心理學》雜志2002年刊載的一項研究顯示，那些停止使用毒品的人在31天后會有抑郁和緊張的感覺。
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