Truth serum ought to be a weapon in our antiterror arsenal.

As Washington warns of impending terrorist attack, potentially with weapons of mass destruction, hundreds of Taliban and al Qaeda detainees and suspects are sitting mum in their cells. According to news reports, they just won't talk.

With so much at stake, the U.S. should use all reasonable means available to get pearls of intelligence out of the clammed-up captives. But the interrogators have been barred from using one of most obvious tools--truth serum. Despite the advocacy of former CIA and FBI director William Webster, the serum has not been used out of concern that doing so would amount to torture. And torture is "cruel and unusual punishment" prohibited by the Eighth and Fifth Amendments, as well as by international law and good conscience.

But the use of truth serum has more in common with wiretaps and other forms of surveillance than it does with torture. Used to search for hidden information about criminal activity, it would more sensibly be governed by the "unreasonable search and seizure" clause of the Fourth Amendment which, unlike the constitutional ban on torture, allows the intrusiveness of the search to be weighed against the gravity of the threat and the urgency of discovering information.

Torture inflicts physical or psychological suffering. Truth drugs--such as sodium pentathol and sodium amytal--are actually powerful pain-killers, invented for use as general anesthetics during surgery. Not only do they not hurt, they tend to make the subject feel giddy, while exercising a tongue-loosening effect akin to alcohol. Cruel and unusual punishment this is not.
While getting someone intoxicated to tell all might not be sporting, it is certainly not brutal. Criminal suspects who want to prove their innocence have been known to volunteer for interrogation under the influence of truth drugs, just as they do for polygraphs. These volunteers would be hard to account for if truth drugs were the chemical version of thumbscrews.

Cops can search a suspect's pockets and his house if they have good reason to think he is hiding evidence of criminal activity. But under the Fourth Amendment, the fact that the information is concealed in a person, not a building, does not bar investigators from taking appropriate measures to look for it--especially when the basis for suspicion is strong, and the likely costs of inaction high.

Police routinely perform body-cavity searches on people suspected of hiding contraband, a type of search upheld by the Supreme Court in 1979 in Bell v. Wofish. Today, we routinely tolerate such searches just to prevent an extra baggie or two from being added to the nation's vast cocaine supply. These justifications pale in comparison to the goal of frustrating terrorist outrages that could kill tens of thousands.

We need not worry about the prospect of people being imprisoned based on confessions wheedled out of them while under the influence of drugs. Information obtained through such interrogations would be used only to disrupt terrorist activities; it would never be used as evidence to prosecute the subject. The Supreme Court ruled 40 years ago that confessions obtained under truth serums can't be used to incriminate the subject.

To be sure, both body-cavity searches and truth serum represent substantial invasions of privacy in the name of law enforcement. But it is hard to say that a subject experiences any greater humiliation or sense of violation from the latter investigative technique than the former. Some make the case that mental privacy is sacrosanct, and under no circumstances should the government probe suspects' minds. But a polygraph does just that, and its investigative use has been upheld by the courts. And criminal suspects can be forcibly given psychoactive drugs when doing so serves an "essential government policy" such as pacifying a violent suspect, or making an insane suspect fit to stand trial.

International lawyers argue that the U.S. must set an example for the world through its treatment of prisoners; that as we treat our prisoners, so will U.S. soldiers be treated upon capture. Given that al Qaeda murdered Navy SEAL Neil Roberts hours after they captured him, we could only hope to be so lucky.

We are repeating the mistakes of August 2001. We have a host of suspected terrorists in custody. We have reason to suspect imminent attack. And the same fear of overstepping legal lines that kept the FBI from searching Zacarias Moussaoui's computer back then keeps the government from searching the memories of the terrorists now. But today there is even less excuse. Now the threat is more real and the legal objections more illusory.

Mr. Kontorovich will be an assistant professor of law at George Mason University Law School starting next academic year.