The first thing to note about "truth serum" -- the sort of substance that Colorado prosecutors have permission to use on Aurora shooter James Holmes should he plead insane -- is that it has little to do with truth-telling.
Judge William Sylvester did not in so many words grant the use of truth serum on Holmes, because truth serum is the stuff of Hogwarts and not juridical determinations. What Sylvester granted was that a "narcoanalytic interview" could be employed to determine if Holmes is genuinely insane. This would entail injecting the accused mass murderer with gradual doses of a barbiturate (most likely sodium amytal) while prosecutors subject him to questioning.
Like taking other barbiturates (or even just a few too many stiff drinks), sodium amytal (also known as sodium amobarbital) can function to lower inhibitions and prompts willingness to talk. In his column on "'Truth serum' and 'what really happened'," psychiatrist August Piper detailed how narcoanalytic interviews typically proceed:
During an Amytal interview, the physician administers small amounts of the drug, by vein, every few minutes. The procedure usually takes about an hour. The patient is drowsy and slurred of speech, but awake -- the so-called "twilight state" for the duration of the interview. Intravenous Amytal causes a feeling of relaxation, warmth, and closeness to the interviewer; while in this state, the patient is questioned. Other intravenous drugs, like Valium or Ativan, are sometimes used in this kind of procedure. For our purposes, these medicines should be considered essentially identical to IV Amytal, because they produce these same effects on the patient.
Piper stresses, however, that amytal's inhibition-lowering effects in no way prompt the subject to offer up true statements or memories. Psychology Today's Scott Linfield noted, per Piper, that "there's good reason to believe that truth serums merely lower the threshold for reporting virtually all information, both true and false. As a consequence, like other suggestive therapeutic procedures, such as guided imagery, repeated prompting, hypnosis, and journaling, truth serums can actually increase the risk of false memories - memories of events that never occurred, but are held with great conviction."
But with the Holmes case, accurate memories are not what's at stake -- whether the 25-year-old can make a legitimate insanity plea is. "Prosecutors would use ["truth serum"] 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," noted Slate's Brian Palmer, adding, however, that the Colorado judge's decision is odd since "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."
Palmer wrote that sodium amytal 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 ethical issues appear glaring around the administration of a drug for nonmedical purposes, with questionable efficacy for the court's stated purpose. Defense attorneys have already filed a motion opposing the narcoanalytic interview, but the judge has signed the order permitting it.
Talking to ABC News, Alison Winter, a professor of history of science and medicine at the University of Chicago, detailed the outdated models of mind and memory that continued reliance on "truth serum" reflects. "Understanding of memory has shifted a lot over the years," Winter said, adding, "The idea that the truth about what a person is like or the truth about what they did is just sitting inside their body waiting to be almost surgically extracted ... it is just so enticing if you desperately need that information ... So I think we keep coming back to it, but then we also keep rejecting it."