On a neurochemical level, nicotine induces a variety of central nervous system, cardiovascular, and metabolic effects. Nicotine stimulates the release of many neurotransmitters, which have been associated with the effects shown in this image:

    Most of these effects are perceived positively by tobacco users, and therefore nicotine induces a constellation of effects that reinforce tobacco use behavior.

    Dopamine Reward Pathway

    Drugs such as cocaine, heroin, amphetamine, and nicotine exert profound effects on the brain. These agents have in common the ability to stimulate the release of the neurotransmitter dopamine in the midbrain. Dopamine induces feelings of euphoria and pleasure and is responsible for activating the dopamine reward pathway.

    The dopamine reward pathway, as depicted in this simplified diagram, is a network of nervous tissue in the middle of the brain that elicits feelings of pleasure in response to certain stimuli. The important interconnected structures of the reward pathway include the ventral tegmental area (VTA), the nucleus accumbens, and the prefrontal cortex (area of the brain responsible for thinking and judgment). The neurons of the VTA contain the neurotransmitter dopamine, which is released in the nucleus accumbens and in the prefrontal cortex.

    Behaviors that naturally stimulate the reward pathway include eating to relieve hunger, drinking to alleviate thirst, or engaging in sexual activity. On a primitive, neurochemical level, stimulation of the reward pathway reinforces the behavior so that it will be repeated. Obviously these behaviors are necessary for continued survival of the organism. The reward pathway can also be stimulated by drugs of abuse such as cocaine, opiates, amphetamine, and nicotine. When these unnatural stimuli trigger the reward pathway the same pleasurable feelings are elicited. Researchers believe that, with chronic drug use, the brain becomes chemically altered—transforming a drug user into a drug addict.

    Consider cigarette smoking as an example. Immediately following inhalation, a bolus of nicotine enters the brain, stimulating the release of dopamine, which induces nearly immediate feelings of pleasure and relief of symptoms of nicotine withdrawal. This rapid dose-response reinforces and perpetuates the smoking behavior.