Armed servicemen of the Vietnam War used drugs more heavily than any previous generation of enlisted U.S. troops. From heroin to amphetamines to marijuana, drugs were so commonplace among the troops that, in 1970, liaison to the Bureau of Narcotics and Dangerous Drugs Egil Krogh told President Richard Nixon “you don’t have a drug problem in Vietnam; you have a condition. Problems are things we can get right on and solve.”

What drugs did soldiers use in the Vietnam War?

According to a 1971 report by the Department of Defense, 51 percent of the armed forces had smoked marijuana, 31 percent had used psychedelics, such as LSD, mescaline and psilocybin mushrooms, and an additional 28 percent had taken hard drugs, such as cocaine and heroin. But drug usage wasn’t just limited by what enlistees could illicitly buy on the black market. Their military command also heavily prescribed pills to the troops under the auspices of improving performance.

According to a report by the House Select Committee on Crime, the armed forces used 225 million tablets of stimulants between 1966 and 1969. In addition to those amphetamines, which were used to boost endurance on long missions, sedatives were prescribed to help relieve anxiety and prevent mental breakdowns. It seemingly worked. In Vietnam, the rate of mental breakdowns in soldiers was 1 percent, a massive reduction from the Second World War (10 percent).

In his book Shooting Up: A Short History of Drugs and War, Lukasz Kamienski argues that amphetamine withdrawal may be partly to blame for some of the atrocities committed against Vietnam’s civilian population, with strung-out young servicemen overreacting to the already stressful conditions of war.

Still, it was the use of illegal drugs—notably heroin and marijuana—that commanded the most media attention during the conflict.

Why were marijuana and heroin so common in Vietnam?

According to Jeremy Kuzmarov, author of The Myth of the Addicted Army: Vietnam and the Modern War on Drugs and an American history professor at the University of Tulsa, there were multiple reasons for widespread drug use in Vietnam: It was “in part because we had the counterculture [stateside], in part because of the ready supply of the drugs, and in part because of the breakdown in morale in the Army, where a rebellion took root.”

Marijuana’s widespread usage came first, with soldiers easily securing the psychotropic substance in villages, where a carton’s worth might sell for five dollars, or else be bartered for with packs of cigarettes. At first marijuana was tolerated by military command. That changed when John Steinbeck IV, a Vietnam soldier and son of the Nobel-prize winning author, wrote an article for Washingtonian magazine in January 1968 about the common use of marijuana among the troops, setting off a media firestorm. In response to the scrutiny, the Army began clamping down on marijuana usage, arresting roughly 1000 G.I.s per week for marijuana possession, while also searching out and destroying marijuana-growing fields with the help of South Vietnamese troops.

The unintended consequence: many G.I.s shifted their drug use to heroin, which was odorless and thus harder to detect. Heroin started flowing more freely into Vietnam from Cambodia in 1970, a consequence of that nation’s civil war. According to a Pentagon study, by 1973 up to 20 percent of soldiers were habitual heroin users. Noting the negative consequences of stifling marijuana use, one army commanding officer was quoted saying, “If it would get them to give up the hard stuff, I would buy all the marijuana and hashish in the Delta as a present.”

VIDEO: VIETNAM BY THE NUMBERS Who went, how much they fought, how many died—and more.

Was drug use by soldiers an important factor in America losing the Vietnam War?

By the time Richard Nixon became president, public opinion around the war in Vietnam was deeply divided. In contrast, President Nixon’s war on drugs enjoyed broad bipartisan appeal, and public officials from both the left and the right were quick to blame marijuana and heroin for American failures abroad. Democratic Senator Thomas J. Dodd claimed illegal drug use directly contributed to the My Lai massacre and other American atrocities of war, stating that, “tens of thousands of troops have gone into battle high on marijuana, opium or other drugs, with horrifying results.”

Despite the rhetoric, military high command found scant evidence that drugs had adversely impacted the fighting. A 1968 survey of unit commanders unanimously concluded that neither marijuana nor any other hard drug had “degraded the military’s combat effectiveness.” General William C. Westmoreland’s headquarters came to a similar conclusion after interviewing several high-ranking officers: “The total scope of the problem is best described as minor.”

Kuzmarov argues that’s because, while drug use was indeed rampant, fears about addiction were largely overblown, with most soldiers only using drugs casually, when they deemed a situation sufficiently low-risk—such as when they were on rest and recuperation leave and during lulls in combat.

“It was just a mechanism of escape from the social conditions of the war,” Kuzmarov says.

Did Vietnam veterans struggle with drug addiction after returning?

There was some public concern that habitually using soldiers would return from Vietnam and abuse drugs at home. In response to that anxiety, the White House implemented “Operation Golden Flow” in 1971, which mandated that all servicemen subject themselves to urinalysis before boarding planes back to the United States. Should a serviceman fail to pass his drug test, he was required to stay in the country for detoxification, only to be released back to the United States upon successfully testing clean.

Anxiety about mass addiction returning to America’s shores proved misplaced. Whether a result of Operation Golden Flow or a sign of the more casual usage than initially reported, an interview survey commissioned by the White House’s Special Action Office for Drug Abuse Prevention found that usage and addiction rates “essentially decreased to pre-war levels” following the soldiers’ return.