Nicotine addiction

Nicotine is a drug that can result in dependence and subsequent difficulty with Nicotine withdrawal.

Modern research shows that nicotine acts on the brain to produce a number of effects. Specifically, research examining its addictive nature has been found to show that nicotine activates the mesolimbic pathway ("reward system") – the circuitry within the brain that regulates feelings of pleasure and euphoria.

Dopamine is one of the key neurotransmitters actively involved in the brain. Research shows that by increasing the levels of dopamine within the reward circuits in the brain, nicotine acts as a chemical with intense addictive qualities. In many studies it has been shown to be more addictive than cocaine and heroin. Like other physically addictive drugs, nicotine withdrawal causes downregulation of the production of dopamine and other stimulatory neurotransmitters as the brain attempts to compensate for artificial stimulation. As dopamine regulates the sensitivity of nicotinic acetylcholine receptors decreases. To compensate for this compensatory mechanism, the brain in turn upregulates the number of receptors, convoluting its regulatory effects with compensatory mechanisms meant to counteract other compensatory mechanisms. An example is the increase in norepinephrine, one of the successors to dopamine, which inhibit reuptake of the glutamate receptors, in charge of memory and cognition. The net effect is an increase in reward pathway sensitivity, the opposite of other addictive drugs such as cocaine and heroin, which reduce reward pathway sensitivity. This alteration in neuronal chemistry can persist for months following the last administration.

A study found that nicotine exposure in adolescent mice retards the growth of the dopamine system, thus increasing the risk of substance abuse during adolescence.