How can my environment affect my response to drugs and alcohol?

The social and environmental context within which a person uses a psychoactive substance (any substance that changes your mood, thinking, or behavior) or engages in a rewarding activity—what psychologists call the "setting"—alters the subjective effect of the substance or activity. Having two beers at home in front of the TV, for example, might make a person sleepy. The same two beers at a party, on the other hand, might make the same person feel excited and free of inhibitions.

A more extreme example is that of the thousands of Vietnam veterans who regularly used heroin during their time at war. While in Vietnam, these soldiers were dependent upon heroin, but when they returned to the United States and left the devastation of war behind, the vast majority (about 90%) of them also quit using heroin.

Part of the reason psychoactive substances can have such situation-specific effects is that physiology can change to match the context. Soldiers who are in active combat, for example, produce a lot of adrenaline and other stress hormones. Those hormones in turn change the chemistry of the brain, possibly making it more vulnerable to addiction within that setting.