“We had the best amphetamines available and they were supplied by the U.S. government,” said Elton Manzione, a member of a long-range reconnaissance platoon (or Lurp). He recalled a description he’d heard from a navy commando, who said that the drugs “gave you a sense of bravado as well as keeping you awake. Every sight and sound was heightened. You were wired into it all and at times you felt really invulnerable.” Soldiers in units infiltrating Laos for a four-day mission received a medical kit that contained, among other items, 12 tablets of Darvon (a mild painkiller), 24 tablets of codeine (an opioid analgesic), and six pills of Dexedrine. Before leaving for a long and demanding expedition, members of special units were also administered steroid injections.

Research has found that 3.2 percent of soldiers arriving in Vietnam were heavy amphetamine users; however, after one year of deployment, this rate rose to 5.2 percent. In short, the administration of stimulants by the military contributed to the spread of drug habits that sometimes had tragic consequences—because amphetamine, as many veterans claimed, increased aggression as well as alertness. Some remembered that when the effect of speed faded away, they were so irritated that they felt like shooting “children in the streets.”

Psychoactive substances were issued not only to boost the fighters, but also to reduce the harmful impact of combat on their psyche. In order to prevent soldiers’ mental breakdowns from combat stress, the Department of Defense employed sedatives and neuroleptics. By and large, writes David Grossman in his book On Killing, Vietnam was “the first war in which the forces of modern pharmacology were directed to empower the battlefield soldier.” For the first time in military history, the prescription of potent antipsychotic drugs like chlorpromazine, manufactured by GlaxoSmithKline under the brand name Thorazine, became routine. The massive use of psychopharmacology and the deployment of a large number of military psychiatrists help explain the unprecedentedly low rate of combat trauma recorded in wartime: Whereas the rate of mental breakdowns among American soldiers was 10 percent during the Second World War (101 cases per 1,000 troops) and 4 percent in the Korean War (37 cases per 1,000 troops), in Vietnam it fell to just 1 percent (12 cases per 1,000 troops).

This outcome, however, was short-sighted. By merely alleviating soldiers’ symptoms, antipsychotic medicines and narcotics brought immediate but temporary relief. Drugs taken without proper psychotherapy only assuage, suppress, or freeze the problems that remain deeply embedded in the psyche. Years later, those problems can explode unexpectedly with multiplied force.

Intoxicants do not eliminate the causes of stress. Instead, observes Grossman, they do “what insulin does for a diabetic: They treat the symptoms, but the disease is still there.” That is precisely why, compared with previous wars, very few soldiers in Vietnam required medical evacuation because of combat-stress breakdowns. By the same token, however, the armed forces contributed to the unprecedentedly widespread outbreak of PTSD among veterans in the aftermath of the conflict. This resulted, to a large extent, from reckless use of pharmaceuticals and drugs. The precise number of Vietnam veterans who suffered from PTSD remains unknown, but estimates range from 400,000 to 1.5 million. According to the National Vietnam Veterans Readjustment Study published in 1990, as many as 15.2 percent of soldiers who experienced combat in Southeast Asia suffered from PTSD.