“Truth serums,” despite how they’re often depicted in films and on TV, aren’t magic potions that force a person to tell the truth. They’re basically drugs that alter your cognitive functioning ability. By that definition, one could say that many people self-administer truth serums every weekend -- it's not for nothing that we say in vino veritas.
A more strictly defined category of psychoactive truth serums includes sedatives and sleep-inducers like the anti-sea-sickness drug scopolamine, and benzodiazepines like the insomnia treatment temazepam.
One of the more famously known truth drugs is sodium thiopental, also known as sodium pentothal. The drug, which is also used in lethal injections, is a barbiturate that decreases brain functioning. The logic behind using it as a truth serum is that lying requires more thought than truth-telling, so weakening a person’s higher-level thinking will make it hard for them to lie.
If Holmes, who’s accused of killing 12 and wounding dozens more last July, does undergo what the practitioners call a “narcoanalysis,” the drug of choice will likely be sodium pentothal or sodium amytal.
Though there have been numerous papers on the science of lie detection, there are no large, randomized controlled trials proving that “truth serums” work. The practice of using truth serums has largely died out in modern courts, which made Judge William Sylvester’s decision to allow it in Holmes's case all the more eyebrow-raising.
"The idea that sodium amytal is a truth serum is not correct," Columbia University psychiatrist Steven Hoge told ABCNews.com. "It's an invalid belief. It is unproven in its ability to produce reliable information and it's not a standard procedure used by forensic psychiatrists in the assessment of the insanity defense, nor is polygraph."
Prosecutors will be watching for signs that he’s faking a mental illness, also known as “malingering.”
A drug like sodium amytal “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,’” Slate writer Brian Palmer explains. “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.”
Slate points out that sodium amytal has been used in insanity plea cases before, but usually with the reverse aim of proving insanity -- while both sober and drugged, one convicted murderer maintained his delusions about visions of a demonic figure appearing before he shot his girlfriend.
In addition to the lack of evidence supporting the effectiveness of narcoanalysis, many doctors say the participation of psychiatrists and other medical professionals in the administration of “truth serums” is troubling from a bioethical standpoint. Most medical ethics guidelines stipulate that health personnel should not assist in interrogations of prisoners that have the potential to affect their mental or physical health.
In a scathing 2007 editorial in the Indian Journal of Psychiatry, psychiatrist Anirudh Kala laid out the troubling rise of narcoanalysis in the post-9/11 age.
“Why are mental health professionals being such willing partners to something which is neither scientific nor ethical?” Kala wrote. “The answer, I do think, is plain and simple narcissism. You get to wear white coats on TV and save the nation from serial killers at the same time.”