The main adverse effect of nicotine is addiction, which sustains tobacco use. Because most smokers are nicotine-dependent, they continue to expose themselves to toxins from tobacco. Tobacco, not nicotine, is responsible for most of the adverse health effects.

Nicotine is a highly addictive drug, as addictive as heroin or cocaine when delivered by means of tobacco products (USDHHS, 1988). Nicotine is used by tobacco users to modulate mood and arousal, as well as for pleasure. Upon cessation of tobacco use, withdrawal symptoms develop, which are generally unpleasant and often disruptive to daily life. The addictive effect of nicotine (including conditioned reinforcement effects) sustains tobacco use. In the absence of nicotine, it is unlikely that sustained smoking behavior would be supported over the long-term. Conversely, nicotine-containing medications (termed nicotine replacement therapy) can be used instead of tobacco to aid quitting. The addiction risk of nicotine in medications has proved to be very low compared to the risk posed by tobacco products (USDHHS, 1998; Benowitz, 1998; Royal College of Physicians, 2000). While people use tobacco for the effects of nicotine, they suffer adverse health consequences, mainly from damage caused by tar, oxidizing chemicals, carbon monoxide and other constituents of tobacco or tobacco smoke (Hoffmann & Hoffmann, 1997; Smith et al., 2003).

Nicotine has long been believed to be one of the major toxins that contributed to tobacco-related disease. However, the myriad of other toxins in cigarette smoke are responsible for the majority of the harmful effects (Benowitz, 1998; Benowitz, 2003; Hatsukami et al., 2006; Hecht et al., 2006; Murphy et al., 2004). In other words, it is the delivery system, not the addictive drug, which is responsible for the vast majority of tobacco-related disease. More detailed information on the effects of nicotine on cardiovascular disease and pregnancy are discussed in the commentaries on other key findings in the section.

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