What is addiction
An addiction is the continued use of a mood altering substance that can give pleasurable sensations is even though its use becomes compulsive resulting in dependency, loss of control over use of the substance and interference with aspects of life such as work and relationships. With continued use the body becomes tolerant as it adapts to the effects of the addictive substance, which means that more of the substance is needed to give the same reward and this begins the addiction cycle.
Nicotine addiction and dopamine
Nicotine is one of the most addictive drugs and causes a physiological dependency within a very short time after first use. Within seconds of inhalation, nicotine reaches the brain and stimulates release of several neurotransmitters. Nicotine activates the dopamine pathway in the brain by binding to the nicotinic acetylcholine receptor resulting in increased dopamine levels. Dopamine is the neurotransmitter that controls the reward and pleasure centres in the brain and is responsible for reward-driven behaviour. Feelings of pleasure created by dopamine reinforce the behaviour that created the pleasurable feeling, which in the case of nicotine is to continue smoking to be rewarded by the feeling of relaxation and euphoria, which leads to nicotine addiction.
Nicotine stimulates other neurotransmitters, including, noradrenaline that acts as a stimulant increasing heart rate, as well as suppressing appetite; acetylcholine that increases heart rate, muscle movement and cognition, which is why many smokers feel an increase of energy or an increase in ability to concentrate directly after smoking a cigarette. Nicotine also triggers the release of brain endorphin, which is a natural analgesics and “feel good” hormone. Nicotine also increases release of serotonin and when serotonin activity falls, this triggers the craving for another cigarette.
Tolerance and withdrawal
As the effect of nicotine wears off, craving for another cigarette to reinforce the pleasurable feelings associated with nicotine use is triggered. Also more nicotine is needed to achieve the same level of reward. Continued use of nicotine to satisfy the craving leads to tolerance and dependency and so the addiction cycle continues.
If the craving for nicotine is not satisfied the brain reacts to lack of stimulation by nicotine by going into withdrawal and this creates withdrawal symptoms. Symptoms include irritability, restlessness, anxiety, increased appetite, difficulty concentrating, sleep disturbances and constant craving for another cigarette.
Medication for nicotine withdrawal symptoms
Buproprion is an antidepressant drug that acts directly on the brain in a similar way to the SSRI and SNRI antidepressants by increasing the amount of serotonin and noradrenaline, however, but is not selective because it also increases the amount of catecholamines and dopamine. Buproprion also binds to the nicotinic acetylcholine receptor, which blocks the action of nicotine and reduces the reward effects of nicotine. Buproprion is used as part of a smoking cessation programme to help break smoking addiction, by reducing the urge to smoke and counteracting withdrawal symptoms.