Nicotine has long been known to be a risk factor for cardiovascular disease and cancer, but it also is a gateway to substance abuse and marijuana, and a factor in mental illness. The National Center on Addiction and Substance Abuse at Columbia University has now published Tobacco -- The Smoking Gun (for purchase or free pdf download) discussing the damage done to the adolescent brain.
Anxiety symptoms are stronger for smokers than for non-smokers, and twice as many (22 percent) nicotine-dependent people with anxiety disorders smoke compared to the general population (11 percent). But the direction of smoking and illness is not always clear. Some studies indicate that while smoking “points to an increased risk of depression,” depression might also be a risk factor for smoking.
Animal studies suggest that nicotine exposure causes serotonin impairment, and people with depression have “a decrease in these receptors.” Nicotine also produces neurochemical reactions in the developing brain including an increased amount of dompamine.