Why people smoke
Physical and psychological effects of nicotine
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.
Arterial and venous levels of nicotine during cigarette smoking
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.
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.
Pathways of nicotine reinforcement and addiction. Adapted from Watkins
et al. Nicotine and Tobacco Research 2000;2:19-37
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.
Smoking behaviour and cessation
- The natural course of cigarette smoking is typically characterised by the onset of regular smoking in adolescence, followed by repeated attempts to quit
- Each year about a third of adult smokers in the United Kingdom try to quit, usually unaided and typically relapsing within days
- In general, less than 3% of attempts to quit result in sustained (12 months’) cessation, though the chances of success are slightly higher in women of childbearing age, parents of young children, and spouses of non-smokers
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.