- Andrew Molyneux, specialist registrar in respiratory medicine
- City Hospital, Nottingham
Although products for nicotine replacement therapy (NRT) have been available for over 20 years, they have been excluded until recently from state or insurance based health service provision in the United Kingdom and many other countries. They have therefore not been widely prescribed by doctors who help smokers wanting to quit. Recent changes in funding policy in the United Kingdom and new guidance from the National Institute for Clinical Excellence (which covers England and Wales) mean that NRT products can and should now be made available to all smokers who want to stop smoking. Like other pharmacological interventions for helping smokers to quit (see the next article in this series), NRT is most effective when used in conjunction with behavioural and other types of non-pharmacological cessation interventions.
Mechanism of action
The main mode of action of NRT is thought to be the stimulation of nicotinic receptors in the ventral tegmental area of the brain and the consequent release of dopamine in the nucleus accumbens. This and other peripheral actions of nicotine lead to a reduction in nicotine withdrawal symptoms in regular smokers who abstain from smoking.
NRT may also provide a coping mechanism, making cigarettes less rewarding to smoke. It does not completely eliminate the symptoms of withdrawal, however, possibly because none of the available nicotine delivery systems reproduce the rapid and high levels of arterial nicotine achieved when cigarette smoke is inhaled.
All the available medicinal nicotine products rely on systemic venous absorption and do not therefore achieve such rapid systemic arterial delivery. It takes a few seconds for high doses of nicotine from a cigarette to reach the brain; medicinal products achieve lower levels over a period of minutes (for nasal spray or oral products such as gum, inhalator, sublingual tablet, or lozenge) and hours (for transdermal patches).