Does truth serum work?

Previously published Slate articles made new.
Dec. 4 2008 11:39 AM

Does Truth Serum Work?

Or is it all lies?

Indian police announced Wednesday that they'll be administering a "truth serum" to the sole Islamic militant captured during last week's terror attacks on Mumbai. How effective are truth serums? In 2001, Chris Suellentrop investigated. The article is reprinted below.

Illustration by Robert Neubecker.

Four suspected terrorists refuse to talk about what they know about Sept. 11 and Al Qaida's plans for the future, the Washington Post reports: Zacarias Moussaoui, the French Moroccan who wanted to learn how to fly jets but not how to land them; Mohammed Jaweed Azmath and Ayub Ali Khan, the two Indians who deplaned in St. Louis on the morning of Sept. 11 when all flights were ordered to land and were detained the next day in Fort Worth, Texas, after they were found with box cutters, hair dye, and $5,000 in cash; and Nabil Almarabh, a former Boston cabdriver thought to have ties to Al Qaida. A former senior FBI official proposed that investigators could use a "truth serum" to get the four suspects to talk. Does truth serum work?

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Not in the sense that it makes people tell the truth. So-called truth serums lower your inhibitions, and as a result you may become chattier but not necessarily more truthful. Losing your inhibitions isn't the same as losing your self-control. Subjects who have been administered a "truth serum" can lie, they can fantasize, and they can be manipulated into telling falsehoods by an interviewer's suggestions and cues.

Depressants   such as scopolamine, sodium amytal, and sodium pentothal were first touted as truth serums in the early 20th century. * Because they inhibit control of the central nervous system, truth serums were supposed to induce a hypnotic "twilight" state that elicited a mechanical recitation of truth. In reality, though, the only good truth serums are found in bad science fiction.

Researchers could have found a much older (and equally unreliable) claim of truth-telling for a similar drug in the old phrase in vino veritas. As Lindsey vs. United States, a 1956 federal appeals court decision, found, "The intravenous injection of a drug by a physician in a hospital may appear more scientific than the drinking of large amounts of bourbon in a tavern, but the end result displayed in the subject's speech may be no more reliable." If a terrorist has something he wants to get off his chest, he may be more apt to tell you about it while drunk or drugged. But you might learn about his propensity to wear his mother's burqa when he was a child, or his sinful crush on Madonna, and not his plan to blow up the Eiffel Tower. Or he may tell you lies, or he may tell you nothing at all.

The Supreme Court decided in 1963 that a truth serum-induced confession was unconstitutionally coerced. More recently, state courts have found truth serum-induced testimony to be scientifically unreliable and inadmissible.

Explainer addendum: Just because the Supreme Court rejected the use of truth serum in the past doesn't mean it will in the future. As Explainer pointed out recently, the Supreme Court wrote in June that terrorism may require "heightened deference to the judgments of the political branches with respect to matters of national security." So the former FBI official quoted by the Post could be right that "you could reach a point where they allow us to apply drugs to a guy." But that doesn't mean that applying drugs to a guy would necessarily do any good.

Got a question about today's news? Ask the Explainer.

Correction, Nov. 10, 2009: The original described scopolamine as a barbiturate. It's actually a tropane alkaloid. (Return to the corrected sentence.)

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