Editor's note: Arthur Caplan is the Drs. William F. and Virginia Connolly Mitty professor and director of the Division of Bioethics at New York University Langone Medical Center.
(CNN) -- Back in the 1950s, Hollywood fell in love with the idea of truth serum. All manner of spies, murderers and other bad guys were given a needle containing sodium pentothal on the big screen and soon were babbling away uncontrollably as to their guilt or complicity with Red China or the Soviet Union.
As recently as 2004 in "Meet the Fockers," a former CIA agent played by Robert De Niro injects his would-be son-in-law, played by Ben Stiller, with the stuff to get the lowdown on his love life. Stiller's character confesses, in a foreshadowing of Arnold Schwarzenegger's amorous ways, to having had a child with his housekeeper, although whether he did or not is far from clear.
Harry Potter knew all about truth serum. Veritaserum was used on a variety of miscreants and by evildoers. It was so powerful and feared that its use was strictly controlled by the Ministry of Magic.
In reality, magical thinking is all it really is. There is no such thing as truth serum. But that news has apparently not reached Colorado. The judge in charge of the mass murder trial of James Holmes seems to think Hollywood was onto something with its fascination with truth serums.
He has approved the use of a "narcoanalytic interview" -- such as a "truth serum" like sodium pentothal -- as part of a competency evaluation to determine whether Holmes was legally insane at the time he allegedly went on a rampage in a theater in Aurora, Colorado. Holmes is charged with killing 12 people and injuring many more.
Sodium pentothal -- the original "truth serum" -- was discovered in 1936 by Ernest H. Volwiler and Donalee L. Tabern working in Chicago at Abbott Laboratories. They were trying to create an injectable drug for use in general anesthesia. Their discovery was a success and had a huge impact on surgery. Sodium pentothal is still used today to knock out patients before they are given another, longer-lasting anesthetic to keep them unconscious during surgery.
Sodium pentothal made surgery far less painful. It also has an interesting side effect. People under its influence lose their inhibitions and babble on about all sorts of things, leading to some amusing moments for surgical teams. This loss of inhibition gave a few researchers hope that the drug or something like it could be used to get the truth out of people in police stations, security interrogations or trials.
But outside of Hollywood, no drug passes muster as a potion capable of getting accurately at the truth. People do get uninhibited and talk more freely, but they don't necessarily stop lying or fantasizing. They also grow more compliant, tending to agree with those asking them leading questions.
There is no solid evidence that what is said under the influence of a "truth" drug correlates reliably with the truth. For the most part, people yammer away. If anything, they behave as if they were drunk rather than diligently affirming the sober truth.
There is no drug that is going to shed trustworthy light on Holmes' state of mind last year when, police say, he donned a gas mask as well as full body armor and grabbed a rifle, a pump-action 12-gauge shotgun and at least one .40-caliber semiautomatic pistol to launch a heinous attack. No drug can tell us what he was really thinking.
In giving permission to use drugs, the judge has opened the door to a line of defense in which Holmes' lawyers can argue that if drugged, he is being forced to testify against himself against his will.
As much as some might hope for a thing such as a truth serum, none exists. Whether Holmes was bad or mad when he allegedly caused so much misery to so many people will not get resolved by a technique beloved by Hollywood movie directors but not by scientists.
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The opinions expressed in this commentary are solely those of Arthur Caplan.