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Opioids like heroin, morphine, OxyContin, and fentanyl occupy a spot in the public imagination as particularly dangerous and addictive substances. Amid an addiction epidemic with no end in sight, this class of drugs has been given special attention in the news, funding bills, and the 2017 President’s Commission on Combatting Drug Addiction and the Opioid Crisis. But does the evidence justify that view?

One way to find out would be to study a random sample of people living in the same environment, exposed to the same amount of opioids, who can be tested and followed over time. Impossible and unethical, right?

So it would seem. But a study like that actually took place 50 years ago. The unexpected results shed light on the nature of addiction and the position of opioids in an array of other widely misused legal and illegal drugs. It’s too bad this research has been largely forgotten because its lessons can be useful today.


In 1971, President Richard Nixon declared drug abuse the nation’s “No 1. Public Health Problem.” At the time, the military was concerned about soldiers in Vietnam who had easy access to heroin that was cheap and potent. To get a better handle on the problem and see how best to support veterans, the Department of Defense, the National Institutes of Health, and the Veterans Administration funded a research project.

The starting point for this natural experiment was to figure out who had become addicted to heroin. In September 1971, every soldier scheduled to return home had a urine test to check for drug use. Soldiers knew that a positive test meant they would be sent to detox for six to seven days. Based in part on this information, the researchers assumed these men were unable to stop using and had become addicted.


Sociologist Lee N. Robins, who was hired to lead the research project, selected and interviewed a random sample of 470 soldiers from the nearly 14,000 headed home in September 1971, as well as a sample of 495 who had tested positive for opioids. Almost half of all enlisted men in the Army serving in Vietnam had tried one of two opioids — heroin or opium — and 20% had become addicted while there. All had been in the country for one year, so their exposure to the drug-rich environment was essentially the same.

The team’s finding that the availability of a given drug is a key to how much it’s used is obvious and uncontroversial. The rest of what they learned was not.

Eight to 12 months after the soldiers returned to the U.S., Robins and her team conducted confidential interviews and requested urine samples for drug testing. Surprisingly, they learned that heroin use was uncommon, even among those who had become addicted in Vietnam. In the first year back home, only 5% had relapsed to addiction.

Some critics of the study argued that more veterans would relapse after a longer period of time. So two years later, Robins and her team re-interviewed the soldiers and again asked them to provide urine specimens for analysis. The researchers discovered that only 12% had relapsed after three years. The rest had recovered spontaneously without any treatment. The research results were so different from what people expected that the scientific community was skeptical, and the press assumed the study was a Department of Defense whitewash.

Robins wrote that she “found little to justify the view of heroin as an especially dangerous drug.” Instead, some people appear to be more vulnerable to drug abuse in general. Those who became addicted to heroin in Vietnam were more likely to have had social problems before they arrived in the country and used marijuana, alcohol, amphetamines, and other substances while there.

Nor did her team’s analysis show that heroin use was a response to intolerable circumstances, like the stress of war, although her research has recently been advanced as evidence for that idea. Veterans who became addicted to heroin began to use it early in their tours of duty in Vietnam, typically before they were in combat. And, as Robins pointed out, there was no “dose response.” In other words, more time at the frontline didn’t correlate with a greater likelihood of using heroin — which would be expected if the stress of war was to blame. Robins also found that even though some veterans returned to occasional use once they were back home, they did not become addicted again.

“Certainly, our results are different from what we expected in a number of ways,” Robins and her colleagues wrote in 1977. “It is uncomfortable presenting results that differ so much from clinical experience with addicts in treatment.”

For all its strengths, the Vietnam study had its weaknesses. One was that individuals with known mental illness, who are more likely to have substance abuse disorders, were excluded from serving in the Army, so there’s no way to know if they would have relapsed to addiction at higher rates than other veterans.

Nevertheless, the evidence from this 50-year-old study is consistent with what we know about substance use disorders today, such as that polysubstance use remains widespread. Surveys and drug testing show that people who use opioids tend to use other drugs as well, often at the same time.

Similarly, many people recover on their own from drug addictions. Compared to the roughly 20 million people in the United States with active substance use disorders, more than 20 million are in long-term recovery. Most of them did not receive formal treatment.

And finally, exposure to opioids doesn’t inevitably lead to a substance use disorder. Some people can use opioids occasionally without becoming addicted. In fact, a recent analysis found that only about 3% of the tens of millions of people prescribed opioids become addicted.

Americans are right to be concerned about opioids, which can be lethal because they suppress the drive to breathe. This is especially true for the potent opioid fentanyl, which helped drive an alarming rise in overdose deaths in 2020. But to put it in perspective, in 2016, there were roughly 150,000 or more deaths caused directly or indirectly by all drugs combined compared to about 42,000 overdose deaths associated with opioids. And, of course, it’s near impossible to quantify the reduced quality of life experienced by the millions of people who live with substance use disorders.

The U.S. is in the grip of an addiction crisis, not just an opioid crisis. Although the Vietnam study didn’t provide a prescription for ending this epidemic, it did reveal that opioids are just one devastating piece of the puzzle. We should be careful not to focus so closely on those drugs that we don’t see the whole picture clearly.

Lauren Aguirre is a science journalist and author of “The Memory Thief and the Secrets Behind How We Remember — A Medical Mystery” (Pegasus Books, June 2021), from which this essay is adapted.

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