Biological model of addiction
Evidence to suggest addiction is due to mood and emotion genetic vulnerability
Lerman suggested that people without a certain "reward gene" have fewer dopamine receptors and are therefore more likely to become addicts.
Dopamine received special attention due to its role in mood and emotion.
Nicotine has been shown to raise dopamine levels giving a positive feeling - therefore people without the reward gene are more likely to become addicts as nicotine stimulates the few receptors they do have.
Maintenance is due to a chemical addiction. The NRM suggests people maintain smoking because doing without is so unpleasant.
Nicotine provides temporary feelings of pleasure however these are short lived - withdrawal start
Smokers become tolerant and have to smoke more to maintain the same feeling.