Does Truth Serum Really Work?

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March 13 2013 1:20 PM

Too High to Lie

Can truth serum prove that James Holmes is sane?

James Holmes, Aurora theater shooting suspect, sits in the courtroom during his arraignment in Centennial, Colo., on Tuesday, March 12, 2013.
James Holmes, Aurora theater shooting suspect, sits in the courtroom during his arraignment in Centennial, Colo., on Tuesday, March 12, 2013.

Photo by R.J. Sangosti/Pool/Denver Post/AP

A Colorado judge has approved the administration of “truth serum” to accused mass killer James Holmes, should he plead insanity. The unspecified drug would be used to assess Holmes’ state of mind at the time of the shootings and potentially reveal whether he is faking mental illness. Can you prove that someone is sane by drugging them?

Not reliably. The most likely drug that prosecutors would use on Holmes is sodium amobarbital, also known as sodium amytal. It has dozens of psychiatric applications, but it doesn’t seem to do any of them particularly well. In Holmes’ case, prosecutors would use it to prove that he’s malingering, or feigning illness, psychiatric illness in this case. Doctors first attempted to use the chemical for this purpose in the 1940s, when a psychiatrist claimed to get several drugged soldiers to admit their malingering. These days, psychiatrists are less sanguine about the drug’s effectiveness for this purpose. Sodium amobarbital lowers a subject’s defenses, and thus makes it easier to catch him in a lie, but a person can continue to lie under the influence of so-called “truth serum.” In addition, the drug may increase a patient’s susceptibility to suggestion, raising the possibility that a truly disturbed patient could falsely admit to malingering.

To conduct a so-called narcoanalytic interview, psychiatrists put the patient on an intravenous drip of sodium amobarbital until he slurs his speech or shows some other manifestation of the drug’s effects. The questions are easy at first—What is your name? How old are you? Where are you right now?—then progress to the incident the interviewer is focused on. The psychiatrist often uses emotionally evocative questioning to startle the subject into disclosing suppressed memories of the event. While experts debate the procedure’s effectiveness in general, everyone agrees that narcoanalytic interviews are useless on certain people. Some subjects fall asleep before the interviewer gets to the important questions, while others are so punchy that their responses are gibberish.


Sodium amobarbital has been used in insanity pleas before, although usually to prove insanity rather than disprove it. In the late 1980s, for example, attorneys for a New Jersey man who had shot his ex-girlfriend at point-blank range in view of dozens of bystanders used a narcoanalytic interview to have his murder sentence cut in half. In a sober state, the defendant mentioned having visions of the devil but had no memory of the shooting. Under the influence of sodium amobarbital, he claimed that his girlfriend morphed into a horned, flame-breathing devil just before he opened fire. Although the judge didn’t allow the psychiatrists to mention sodium amobarbital or “truth serum” in court, they were permitted to offer their opinions of the defendant’s mental condition, which were based in part on the narcoanalytic interview. (Most judges treat narcoanalytic interviews like polygraph examinations and keep them out of evidence.)

The oddest part of the Colorado judge’s decision to force Holmes to submit to truth serum is that there are better ways to identify malingering, and they don’t require the medical risks and ethical complications of chemical intervention. Psychiatrists typically subject patients to round-the-clock monitoring, because it’s difficult to fake insanity all the time. Interviews go on for hours, testing the malingerer’s endurance and consistency. A useful technique is to suggest highly unlikely symptoms to see if the patient will quickly adopt them. (One doctor suggests asking the patient whether he believes automobiles are “members of an organized religion.”) In general, malingerers tend to be less straightforward in interviews, and fail to exhibit classic psychiatric symptoms that are difficult to fake, like word salad.

Explainer thanks forensic psychologist Elliot Atkins.

Got a question about today’s news? Ask the Explainer

Brian Palmer writes about science, medicine, and the environment for Slate and the Natural Resources Defense Council. Email him at Follow him on Twitter.


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