Did 20% of US soldiers in Vietnam use heroin, 95% of whom quit afterwards?

Question

The following claims were made around 04:50 of this TED talk by Johann Hari:

20 percent of all American troops were using loads of heroin, and if you look at the news reports from the time, they were really worried, because they thought, my God, we're going to have hundreds of thousands of junkies on the streets of the United States when the war ends; it made total sense. Now, those soldiers who were using loads of heroin were followed home. The Archives of General Psychiatry did a really detailed study, and what happened to them? It turns out they didn't go to rehab. They didn't go into withdrawal. Ninety-five percent of them just stopped.

Are the claims true? In other words:

1. Did 20% of US soldiers in Vietnam use "loads of" heroin?

2. Did 95% of the US soldiers who were using "loads of" heroin stop using heroin afterwards?

Answer 1

Yes, the claims are approximately true.

From a 1976 study:

Two stages of Vietnam drug use are identified-a period of increasing marijuana use followed by the 1970 influx of highly potent heroin to which 1/5 of the enlisted troops were addicted at some time during their tour. ... Since 95% of those who were addicted to narcotics in Vietnam have not become readdicted, the situation does not appear to be as severe as originally supposed.

Thus, 20% of US soldiers were addicted to heroin at some point during their tour and 95% of those addicted did not become re-addicted after the war and stopped using heroin.

This 2010 paper more specifically mentions only ~5 percent of Vietnam War veterans who were addicted to heroin took heroin 1 year after the war.¹ The authors also write (emphasis added):

Eighty-five percent of the men told us that they had been offered heroin when they were there—often quite soon after their arrival...Thirty-five percent of Army enlisted men actually tried heroin while in Vietnam, and 19% became addicted to it.

On 15 May 1971 (when the Vietnam War was ongoing, the New York Times published an article using the term "heroin addiction epidemic" chronicling the high use of heroin (emphasis added).

So serious is the problem considered that Ambassador Ellsworth Bunker and Gen. Creighton W. Abrams, the military commander, recently met with President Nguyen Van Thieu on measures to be taken by the Saigon Government, including agreement on a special task force that will now report directly to Mr. Thieu.
...
John Ingersoll, the Director of the Bureau of Narcotics and Dangerous Drugs, also conferred with Mr. Thieu and other officials and returned to Washington, reportedly alarmed at the ease with which heroin circulates and fearful of the danger to American society when the addicted return craving a drug that costs many times more in the United States than it does here.
...
The epidemic is seen by many here as the Army's last great tragedy in Vietnam.
...
Some officers working in the drug‐suppression field, however, say that their estimates [for addiction to heroin] go as high as 25 per cent, or more than 60,000 enlisted men, most of whom are draftees. They say that some field surveys have reported units with more than 50 per cent of the men on heroin.

In the present day, both CNN and NPR write that 15% of US soldiers in Vietnam were addicted to heroin in 1971. From the second source:

In May of 1971 two congressmen, Robert Steele from Connecticut and Morgan Murphy of Illinois, went to Vietnam for an official visit and returned with some extremely disturbing news: 15 percent of U.S. servicemen in Vietnam, they said, were actively addicted to heroin.
...
Soon a comprehensive system was set up so that every enlisted man was tested for heroin addiction before he was allowed to return home. And in this population, Robins did find high rates of addiction: Around 20 percent of the soldiers self-identified as addicts.
...
"I believe the number of people who actually relapsed to heroin use in the first year was about 5 percent," Jaffe said recently from his suburban Maryland home. In other words, 95 percent of the people who were addicted in Vietnam did not become re-addicted when they returned to the United States.

The Huffington Post also quotes both the 15% and 20%. It would appear the 15% statistic is the estimate of 2 congressman whereas the 20% statistic is based on more accurate research after the war.

While visiting the troops in Vietnam, the two congressmen discovered that over 15 percent of U.S. soldiers had developed an addiction to heroin. (Later research, which tested every American soldier in Vietnam for heroin addiction, would reveal that 40 percent of servicemen had tried heroin and nearly 20 percent were addicted.) The discovery shocked the American public and led to a flurry of activity in Washington, which included President Richard Nixon announcing the creation of a new office called The Special Action Office of Drug Abuse Prevention.

To conclude:

Did 20% of US soldiers in Vietnam use "loads of" heroin?

19% of enlisted US soldiers were addicted to heroin "at some time during their tour." 20% is approximately accurate.

Did 95% of the US soldiers who were using "loads of" heroin stop using heroin afterwards?

By 1 year after the war, 95% of the US soldiers addicted to heroin stopped using heroin.

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Why was this the case? The environment was different.

From NPR:

It's important not to overstate this, because a variety of factors are probably at play. But one big theory about why the rates of heroin relapse were so low on return to the U.S. has to do with the fact that the soldiers, after being treated for their physical addiction in Vietnam, returned to a place radically different from the environment where their addiction took hold of them.

"I think that most people accept that the change in the environment, and the fact that the addiction occurred in this exotic environment, you know, makes it plausible that the addiction rate would be that much lower," Nixon appointee Jerome Jaffe says.

From the Huffington Post (emphasis added):

Here is what happened in Vietnam: Soldiers spent all day surrounded by a certain environment. They were inundated with the stress of war. They built friendships with fellow soldiers who were heroin users. The end result was that soldiers were surrounded by an environment that had multiple stimuli driving them toward heroin use. It's not hard to imagine how living in a war zone with other heroin users could drive you to try it yourself.

Once each soldier returned to the United States, however, they found themselves in a completely different environment. Not only that, they found themselves in an environment devoid of the stimuli that triggered their heroin use in the first place. Without the stress, the fellow heroin users, and the environmental factors to trigger their addiction, many soldiers found it easier to quit.

You can read more about the effect of the environment in this excellent article written by Robins (who led the original research time authorized by Nixon).

¹ More specifically, the authors wrote that 1% of interviewees were addicted to heroin a year after the war. If the 1% were all already addicted to heroin (which was true for 19% of interviewees) then 1/19 or 5.26% of interviewees were still addicted to heroin a year after the war. If, instead, not all of the 1% were addicted to heroin in Vietnam then < 1/19 (and > 94.74%) of interviewees who were addicted remained addicted. Thus, the percentage of US soldiers who stopped is at least 94.74%. In the paper cited above, Robins wrote:

In the first year after return, only 5% of [US soldiers] who had been addicted [to heroin] in Vietnam were addicted in the US.

The percent of interviewees addicted to heroin did increase over time.

Answer 2

The first part of the statement is probably true.

The second part is highly misleading. What the actual paper of the time shows is that 5% of former addicts became re-addicted (basically meaning daily use) in the first year, but the number increased to around 10% in two years, and to 12.5% in three years. Furthermore, if we consider relapse as reuse rather than readdiction, the relapse figure in three years was around 50%; this last figure actually agrees with modern studies of opioid-use relapse.

And as a minor quibble the (1975) Arch. Gen. Psych. study on Vietnam did not separate heroin from other narcotics in terms of reuse/readdiction, although subsequent studies by the same main author (in other venues) did. What I wrote above is based on the follow-up studies.

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I don't find the extremely low relapse rate claim plausible. The sources for that from Barry's answer seem to be

• Nixon's drug czar (who obvious has/had a reason to claim addiction is easy to cure); he advanced the exact 5% relapse figure

I believe the number of people who actually relapsed to heroin use in the first year was about 5 percent

• A paper, Robins et al. 2010, originally published in 1977 that was based on army interviews conducted a few years after the veterans returned, which actually says:

It is commonly believed that after recovery from addiction, one must avoid any further contact with heroin. It is thought that trying heroin even once will rapidly lead to readdiction. Perhaps an even more surprising finding than the high proportion of men who recovered from addiction after Vietnam was the number who went back to heroin without becoming readdicted. As Fig. 4 shows, half of the men who had been addicted in Vietnam used heroin on their return, but only one-eighth became readdicted to heroin. Even when heroin was used frequently, that is, more than once a week for a considerable period of time, only a half of those who used it frequently became readdicted.

So basically the trick here is to claim that using heroin again after being addicted (which happened a lot more that 5%) doesn't count because these guys cannot be considered readdicted. This not the same thing as having quit altogether! So this paper is arguing the semantics of re-addiction basically.

Modern statistics of opioid relapse are on par with that (and in dozens of studies). A Cochrane meta-analysis found that using the standard methadone treatment

the majority of patients relapsed to heroin use.

So either Nixon's drug czar was misquoted/misprinted (is that "5%" missing a zero?) or he confused relapse with this army notion of "re-addiction", but even for that the figure was higher than 5%, actually 12.5% is claimed after 3 years.

Also this paper of Robins does support the 20% "used loads of heroid" if by that you mean they were addicted.

One out of five of our sample reported themselves to have been addicted to heroin in Vietnam, and that selfdescription was substantiated by their report of prolonged heavy use and severe withdrawal symptoms lasting more than 2 days. Only 1% of our sample reported addiction to heroin during the first year back from Vietnam, and only 2% reported addiction in the second or third year after Vietnam.

The rather confusing second part of that statement means that around 5% (1/20) of got readdicted (not merely used again) in the first year... but 10% (2/20) got readdicted in two years. There is a bit of rounding error here compared to the 1/8 claim made more explicitly in the previous quote from the same paper.

Also I think this is the part that the drug czar interpreted as 5% relapsed, meaning "relapsed into addiction" rather than "relapse" in the more usual sense of reusing.

The definition of addiction in this Robins paper was entirely based on the user self-reporting himself as such, but for heroin this coincided (in 80% of the subjects) with daily use; see fig 2 in the paper [omitted here] and commentary on it [likewise].

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As an aside, the number of US servicemen using heroin at all (instead of being addicted) was 34% in Vietnam; this from a later (1993) paper of Robins; see fig 1 in that and comments on it. In fact, from the same paper, 38% also used used opium at least once and 45% tried at least one kind of narcotic while over there. (The same paper repeats the 20% figure for addiction, but this time for narcotics instead of just heroin.) Also 80% of Vietnam servicemen used marijuana, according to the same source.

I mention this because the title of the OP's question simply asks about use (unlike the OP's challenged quote which has "loads" as a qualifier.)

And yes, the vague reference to Arch. Gen. Psych. (from the OP quote) almost certainly is the Robins study (which is one and the same, but he wrote about it in multiple venues); the Arch. Gen. Psych. paper is from 1975. The first-year data is more-or-less the same, but this 1975 paper only has data 10 months after the soldiers' return; there's no 2-3 year follow-up like in the 1977 paper. Also this 1975 paper doesn't separate heroin from other narcotics on readdiction/reuse figures:

Men highly dependent on narcotics in Vietnam who said they had been detected as users at departure because they were too addicted to quit had a relatively high risk of use and readdiction after return. But even among these, half stopped narcotic use entirely on return, and only 14% became readdicted (Table 2). Of course, men had been back from Vietnam an average of only ten months at interview, and it is possible that increasing numbers of men will return to narcotic use as time goes on. This seems unlikely, however, since resumption of narcotics generally began within the first four months after return with the median date between the second and third month. Furthermore, of all the men who had used narcotics after return, 84% found a source of supply within eight weeks after return, and men living in all geographical locations in the United States reported ready availability of narcotics.

(In the narcotic category this 1975 study included: codeine, cough syrup, opium, heroine, morphine, and meperidine.)

Its finding ultimately is

After return, usage and addiction essentially decreased to pre-Vietnam levels.

The conclusion from this was elaborated a bit more in the 1993 paper by Robins:

We found little to justify the view of heroin as an especially dangerous drug. [...] Vulnerability to re-addiction if re-exposed may indeed be biological.

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There's also a 25-years-later follow-up study on (mostly) the same sample by another research group. This is actually a very complex study to summarize, because it used much more complicated measures (over time); but it's open access, so you can read it yourselves.

A qualitative conclusion drawn by this latter study is that people who were previously frequent users to opiates had a pretty negative memory of that experience, and subsequently avoided this class of drugs; there were more new cases of frequent use of opiates among veterans (and controls) who didn't have such a prior experience (with opiates) in Vietnam. This is corroborated by the number unpleasant/negative symptoms reported by (former) frequent user of opiates, in contrast to the other drugs considered, like cocaine, or other stimulants, or even other sedatives. Vietnam-era users (of any drug) were much more likely to start frequently using (again) these other non-opiate classes than Vietnam-era drug non-users. So there does seem to be a kind of substitution effect away from opiates. As a teaser, here's the main findings table from this paper, but I won't try to explain all the measures here; it takes pages to do that:

This follow-up study also found that quitting cold turkey any class of drugs worked with high probability (around 90%) among Vietnam-era veterans, according to self-reports.

Also there's another paper by the same authors (Price et al.), which found that a lot more of those Vietnam-era drug users had died by the 25-year follow up, more than the Vietnam drug-nonusers or controls (17.4% vs. 7.4% vs 2.8%). The guys who died were not included in the previously mentioned study on taking up drugs again since it was a retrospective rather than really longitudinal study, so we don't know if the dead took up drugs again (and which) or not.