Smoking: pharmacology

In this section, you’ll see what effects nicotine has in the body and how these effects are produced. You’ll also learn why people become dependent on nicotine and see what withdrawal symptoms may occur if a person who was addicted to nicotine suddenly gave up smoking. Nicotine is the main active ingredient in the tobacco plant, which is widely ingested, normally through smoking, throughout the world in the form of cigarettes, cigars, or pipes. As the only pharmacologically active substance in tobacco smoke, apart from carcinogenic tars and carbon monoxide, smoking is highly addictive. According to the World Health Organisation, addiction to tobacco kills one person prematurely every six seconds.

This is predominately due to the inhalation of tar in the smoke, which contains the most carcinogens, or cancer-causing chemicals. Nicotine being inhaled from a cigarette travels directly to the bloodstream from the lungs. When a cigarette is inhaled, it takes only seconds for the nicotine to reach the brain. Nicotine exerts its effects by binding to nicotinic receptors throughout the body. Nicotinic receptors are ion channels. So when nicotine binds, the ion channels open. And sodium ions rush into the cell and stimulates the cell.

This stimulation of neurons causes some desired effects, such as increased alertness and concentration and reduced anxiety, as well as some unwanted effects, such as an increase in heart rate and sweating. Smokers report that smoking wakes them up when they are drowsy and calms them down when they are tense. However, the effects of nicotine on a person depend very much on whether a person is a first-time smoker or has been smoking for awhile. This is because continual smoking produces tolerance to a number of the effects of nicotine. For example, first-time smokers often become anxious, nauseated and sweaty after smoking, whereas chronic smokers are much less likely to experience these effects.

The tolerance to some effects of nicotine is thought to occur because the receptors become less sensitive to the effects of nicotine. This is called receptor desensitisation.

For a person who has not smoked before, the nicotinic receptors allow many sodium ions into the cell when they open.

However, after a person has been smoking for awhile, the nicotinic receptors become less sensitive and are [INAUDIBLE] less sodium when they open in response to nicotine bonding. This is one reason why smoking is addictive, as the pleasurable effects continue whilst people become tolerant to some of the less pleasant effects. Why people become tolerant to some effects of nicotine and not others is not fully understood. However, it is probably because there are more than one type of nicotinic receptor. And different effects of nicotine are probably the result of activation of different types of nicotinic receptors that have varying degrees of tolerance.

Continually smoking nicotine products results in dependence, which is when a person keeps taking a drug despite problems occurring related to the use of the drug. Let’s now look at nicotine dependence in more detail. It is very difficult to just stop smoking without any assistance. This is because people become dependent on the effects of nicotine. We saw when we discussed morphine in the control of pain that opioids like morphine are more addictive because they release the neurotransmitter Dopamine in the limbic region of the brain. Also in the week we discussed pain, we mentioned the limbic system as an area of the brain important in reward. Nicotinic receptors exist in the limbic system.

And when they are activated by nicotine, Dopamine is released. Drugs liable to being addictive generally share the property of being able to release Dopamine in the limbic system. This is because Dopamine release in the limbic system results in feelings of pleasure. This is reinforcing a person to smoke more. Because smoking is deemed to be pleasurable. So like with morphine, nicotine effectively hijacks the brain’s rewarding system. Because smokers get Dopamine release when they smoke, they crave this feeling when not smoking. If a drug causes dependence because of the reinforcement it provides, this is called psychological dependence. Another key component of nicotine dependence is that smokers associate certain behaviours with smoking.

A smoker becomes used to smoking with certain other activities, such as having a cup of coffee, or after eating a meal, or when socialising with friends. These other activities become environmental cues for the smoker. It is very difficult for an ex-smoker to be in a situation when they would have normally smoked. This is because the cues, such as drinking coffee, have become associated with smoking. And they become reinforcing in terms of smoking, thus take on powerful incentive properties that are critically important for sustaining smoking in humans. We mentioned that smokers become psychologically dependent. But they can also become physically dependent, since they suffer withdrawal symptoms if they stop smoking.

Such symptoms include increased irritability, impaired performance of mental tasks, aggressiveness, and impaired sleep. Even though the physical withdrawal only lasts about two to three weeks, the psychological craving for nicotine products lasts much longer than this. And this is the reason that smokers like Tracy, who’s given up for long periods of time– that is months to years– can suddenly start again. There are various ways in which people try to give up smoking tobacco products. Nicotine replacement therapy, or NRT, is one means of assistance available to tobacco smokers who want to quit, as it reduces physical withdrawal symptoms and the psychological cravings for the drug.

It is most effective when it is combined with psychological interventions designed to help people overcome the psychological aspects of giving up smoking. For example, coping strategies when a person who has been a smoker in a situation in which they would have normally smoked, are very important. Nicotine replacement on its own, without any counselling or support, is not very effective in terms of assisting people giving up smoking. Even with additional support, the success rate of NRT is only about 25%, as defined by the percentage of patients still abstinent after one year. So in this section, you have seen what effects nicotine has in the body and how nicotine produces these effects.

You also saw why people become psychologically and physically dependent on nicotine. You learned what withdrawal symptoms may occur if a person who is addicted to nicotine suddenly gave up smoking, and how nicotine replacement therapy assists people to give up smoking.