Nicotine

It is important to understand how nicotine acts in the brain to keep people smoking. People’s susceptibility to nicotine, and their social and physical environments also play a crucial role in keeping them smoking.

It is explained here in some detail because it is useful to be able to help smokers understand why they are addicted, and why it is difficult to quit smoking.

How nicotine works
Nicotine in cigarette smoke is a drug that mimics a naturally occurring chemical messenger or ‘neurotransmitter’ called acetylcholine which is present in many parts of the nervous system.

Nicotine attaches itself to receptors on nerves in a part of the brain that is important in controlling our motivation, called the ventral tegmental area. This causes the nerve cells to become more active, causing them to release dopamine at the other end of the nerve in an area of the brain called the nucleus accumbens. This process is important in the development and maintenance of addiction.

Nicotine absorption and its elimination from the body
Nicotine from cigarette smoke is rapidly absorbed through the large surface area of the lungs, this results in a nicotine ‘hit’ reaching the brain within a few seconds of each puff.

Following each cigarette nicotine concentrations in the body fall rapidly, as it is metabolised and excreted. The concentration falls by half every 90-120 minutes which means that after a night’s sleep most smokers have very little or no nicotine in the body.

Awareness of how quickly nicotine concentrations fall in the body allows you to understand the onset of withdrawal symptoms and why many smokers need to keep topping up their nicotine levels by smoking regularly throughout the day.

It also explains the significance of knowing how long after waking they have their first cigarette in the morning is as a measure of nicotine dependence.

Nicotine in cigarettes
On average, smokers get just over 1mg of nicotine from each cigarette but the dose varies considerably between smokers. If a cigarette is smoked as hard as possible, a smoker can get up to 6mg nicotine into their system.

Nicotine addiction

Dopamine is released into the brain by the action of nicotine on neuroreceptors, and acts as a ‘chemical reward’ or ‘teaching signal’. The brain naturally seeks out more of this ‘chemical reward’ and does so by motivating us to repeat the behaviour that led to the reward – in this case puffing on a cigarette.

The dopamine mechanism also creates associations between nicotine reward and cues such as:

This link is completely unconscious and undermines the smoker’s ability to make rational choices about the behaviour.

The rapid excretion of nicotine from the body causes withdrawal symptoms, which are quickly relieved by smoking, and this too reinforces their dependence.

Nicotine craving and withdrawals

Smoking causes lasting changes to the brain.

This means that smokers are used to regular doses of nicotine and when there is no, or less, nicotine in the brain, dopamine levels in the nucleus acumbens are abnormally low. This creates what is known as an ‘abnormal drive state’ (much like hunger for food), but in this case the target is nicotine.

It is experienced as a kind of gnawing hunger for a cigarette or ‘craving’.

This is in addition to the cravings triggered by smoking cues.

Habit
Smokers have to ‘learn’ how to smoke because for many, at first it is usually an unpleasant experience with feelings of nausea and giddyness.

However, repeating smoking becomes a habit. Nicotine taps into a part of the brain that learns automatic associations between triggers and actions – the part that learns habits. This means that smokers get automatic impulses to smoke in situations in which they would normally light up, called ‘cues’.

Being in a situation with other smokers, or experiencing events that have previously been associated with smoking, is a high risk time for smokers trying to stop.

When smokers encounter a cue, they have the impulse to reach for a cigarette. If they consciously resist this, they experience the impulse as an ‘urge’ to smoke.

Nicotine withdrawal symptoms
Most smokers will experience unpleasant effects on their mood and physical wellbeing after they quit and this will contribute to their strong desire to smoke

These include: