Several possible explanations of this context-dependent effect of heroin addiction have been proposed. One possibility is that the returning soldiers did not have access to heroin in the United States, limiting their relapse risk. But, the soldiers reported no withdrawal symptoms, which is virtually unheard of in those addicted to heroin in the United States. Another possibility is that heroin addiction is misery-dependent (Hari, 2015). The soldiers were miserable in Vietnam, which led them to use heroin in order to self-mediate the intense pain of their unhappiness. Upon returning to the United States, the soldiers were no longer in a miserable state of intense suffering. They no longer felt the need to use heroin to self-mediate because their misery was specific to the horrors of combat in Vietnam.
Another possibility is that heroin addiction is stimulus bound … i.e., specific to the stimuli that were present at the time that the effects of heroin were experienced. The soldiers experienced heroin’s effects in the combat environment in Vietnam. They were with their combat buddies in the jungles of Vietnam. They were wearing camouflaged jungle fatigues, flack jackets, and combat boots, while carrying weapons, ammunition, and web gear. They were surrounded by the sights, smells, and sounds of war. But, upon returning to the US, none of these wartime stimuli were present. The people, places, and things that were associated with using heroin in Vietnam were simply not present in the United States. This suggests that the overwhelming desire to use heroin observed during a withdrawal episode is due to the presence of stimuli associated with heroin’s effects, and in the absence of these heroin-related cues, the addict does not suffer the overwhelming urges to take the drug.