Smoking cigarettes or using other tobacco products like cigars can affect your sleep in several important ways. It all has to do with the active ingredient, nicotine.
First, depending on your level of use and dependence, your desire for additional nicotine during your sleep may cause you to awaken and this may lead to insomnia. Nicotine itself is a stimulant and the use of it too close to bedtime may also make it difficult for you to fall asleep.
Smoking also is associated with a disruption of the basic structure of sleep called sleep architecture. This is the pattern of sleep stages that occur during the night. In a research study it was shown that current smokers take slightly longer to fall asleep (called the sleep latency), sleep less, and have less deep sleep (called slow wave sleep). For those who quit smoking, these differences in sleep architecture do not persist.
If you smoke and have disrupted sleep, this may be yet another reason why you should quit for your health and well-being.
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Wetter, DW et al. "The relation between cigarette smoking and sleep disturbance." Prev Med 1994; 23:328.
Zhang, L et al. "Cigarette smoking and nocturnal sleep architecture." Am J Epidemiol 2006; 164:529.