Absorption of cigarette smoke from the lung is rapid and complete, producing with each inhalation a high concentration arterial bolus of nicotine that reaches the brain within 10-16 seconds, faster than by intravenous injection. Nicotine has a distributional half life of 15-20 minutes and a terminal half life in blood of two hours. Smokers therefore experience a pattern of repetitive and transient high blood nicotine concentrations from each cigarette, with regular hourly cigarettes needed to maintain raised concentrations, and overnight blood levels dropping to close to those of non-smokers.
Arterial and venous levels of nicotine during cigarette smoking
“If it were not for the nicotine in tobacco smoke, people would be little more inclined to smoke than they are to blow bubbles”
M A H Russell, tobacco researcher, 1974
By age 20, 80% of cigarette smokers regret that they ever started, but as a result of their addiction to nicotine, many will continue to smoke for a substantial proportion of their adult lives
Nicotine has pervasive effects on brain neurochemistry. It activates nicotinic acetylcholine receptors (nAchRs), which are widely distributed in the brain, and induces the release of dopamine in the nucleus accumbens. This effect is the same as that produced by other drugs of misuse (such as amphetamines and cocaine) and is thought to be a critical feature of brain addiction mechanisms. Nicotine is a psychomotor stimulant, and in new users it speeds simple reaction time and improves performance on tasks of sustained attention. However, tolerance to many of these effects soon develops, and chronic users probably do not continue to obtain absolute improvements in performance, cognitive processing, or mood. Smokers typically report that cigarettes calm them down when they are stressed and help them to concentrate and work more effectively, but little evidence exists that nicotine provides effective self medication for adverse mood states or for coping with stress.
A plausible explanation for why smokers perceive cigarettes to be calming may come from a consideration of the effects of nicotine withdrawal. Smokers start to experience impairment of mood and performance within hours of their last cigarette, and certainly overnight. These effects are completely alleviated by smoking a cigarette. Smokers go through this process thousands of times over the course of their smoking career, and this may lead them to identify cigarettes as effective self medication, even if the effect is the negative one of withdrawal relief rather than any absolute improvement.
Figure 3 Pathways of nicotine reinforcement and addiction. Adapted from Watkins et al.
Nicotine and Tobacco Research2000;2: 19-37 [PubMed]