By JOHN TIERNEY -- ALEXANDRIA, Va., March 26 -- The case of the United States v. William Eliot Hurwitz, which began in federal court here on Monday, is about much more than one physician. It's a battle over who sets the rules for treating patients who are in pain: narcotics agents and prosecutors, or doctors and scientists.

Dr. Hurwitz, depending on which side you listen to, is either the most infamous doctor-turned-drug-trafficker in America or a compassionate physician being persecuted because a few patients duped him.

When Dr. Hurwitz, who is now 62, was sent to prison in 2004 for 25 years on drug trafficking and other charges, the United States attorney for Eastern Virginia, Paul J. McNulty, called the conviction “a major achievement in the government's efforts to rid the pain management community of the tiny percentage of doctors who fail to follow the law and prescribe to known drug dealers and abusers.”

Siobhan Reynold, the president of an advocacy group called the Pain Relief Network, hailed Dr. Hurwitz's singular dedication and compared his plight to Galileo's. Some of the country's foremost researchers in pain treatment and addiction supported his appeal for a retrial, which was ordered because the jury in the first case was improperly instructed to ignore whether Dr. Hurwitz had acted in “good faith.” These scientists say they are upset by how their research has been distorted by prosecutors in this case, and suppressed by the Drug Enforcement Administration in its campaign against the misuse of OxyContin and other opioid painkillers.

In the first trial, the prosecution accused Dr. Hurwitz of crossing the line from doctor to trafficker by prescribing irresponsibly high doses of painkillers to his patients in the Virginia suburbs of Washington. He was accused of ignoring blatant “red flags” or signs that some patients were misusing or selling the drugs. That is an emotionally powerful argument for a jury: warning signs can seem perfectly clear with the benefit of hindsight.

But to researchers who study deceptive patients, there is no such thing as a blatant red flag. Deception is notoriously difficult to spot, as Dr. Beth F. Jung and Dr. Marcus M. Reidenberg of Cornell University document in a new survey of the literature. They note, for starters, an experiment showing that even police officers and judges -- ostensibly experts at detecting fraud -- do no better than chance at detecting lying.

Doctors are especially gullible because they have a truth bias: they are trained to treat patients by trusting what they say. Doctors are not good at detecting liars even when they have been warned, during experiments, that they will be visited at some point by an actor faking some condition (like back pain, arthritis or vascular headaches). In six studies reviewed by the Cornell researchers, doctors typically detected the bogus patient no more than 10 percent of the time, and the doctors were liable to mistakenly identify the real patients as fakes.

When treating people with chronic pain, doctors have to rely on what patients tell them because there is no proven way to diagnose or measure it. Also, there is no standard dosage of medicine: A prescription for opioids that would incapacitate or kill one patient might be barely enough to alleviate the pain of another.

During the first trial, the prosecution argued that it was beyond the “bounds of medicine” for Dr. Hurwitz to prescribe more than 195 milligrams of morphine per day, but dosages more than 60 times that level are considered acceptable in a medical textbook. The prosecution's supposedly expert testimony on dosage levels and proper pain treatment for drug addicts was called “factually wrong” and “without foundation in the medical literature” in a joint statement by Dr. Russell K. Portenoy and five other past presidents of the American Pain Society.

Dr. Portenoy, the chairman of the pain medicine department at Beth Israel Medical Center, was one of the researchers who worked with the D.E.A. four years ago to draw up guidelines on pain medication for doctors and law enforcement officials. The guidelines assured doctors that they would be safe unless they “knowingly and intentionally” prescribed drugs for illegitimate reasons, and cautioned narcotics agents not to investigate doctors just because they prescribed large quantities.

The D.E.A. published the guidelines, and then abruptly withdrew them on the eve of Dr. Hurwitz's trial, just after his defense had indicated that it planned to use the document at the trial. The D.E.A., which said the document had not been properly vetted, went on to repudiate some of the guidelines and warned that it intended to keep targeting doctors deemed suspicious because they prescribed large quantities and ignored certain red flags.

Dr. Portenoy, who is to be a witness for Dr. Hurwitz at the retrial, has been one of the pioneers in identifying the risks of prescribing opioids. He says the warning signs that seem so obvious to prosecutors rarely offer clear guidance to doctors. When a patient keeps asking for refills because he runs out of his pills early, does that mean that he is a dealer or that he is not getting enough medication? If a urine test shows the presence of cocaine or other illegal drugs -- as it did in some of Dr. Hurwitz's patients -- should a doctor automatically cut him off? That's what some prosecutors and narcotics agents demand, but doctors realize that there are plenty of illegal drug users who also need pain relief.

“Half of pain patients would have to stop taking their medicine if the rule went out that every so-called red-flag behavior meant you couldn't prescribe,” Dr. Portenoy says. He and researchers like Dr. Steven D. Passik, a psychologist at the Memorial Sloan-Kettering Cancer Center, have found that about half of pain patients exhibit at least a couple of the warning signs, and that even veteran physicians cannot agree on which signs are the most important to look for.

In a pretrial motion, Dr. Hurwitz's lawyer, Richard A. Sauber, asked the court to bar the prosecution's expert witnesses from using the red-flag argument because “it defies reason that any expert could testify” about something without “scientific support.” That motion was denied, however, so the flags may well be waving during the trial.

Even Dr. Hurwitz's supporters acknowledge that he is not the ideal doctor to be the representative for the cause of pain patients. Although his expertise in pain medicine is well respected, some say he was gullible and reckless to the point of incompetence. But the traditional punishments for such mistakes are malpractice settlements and the loss of a state medical license, not a federal investigation and 25 years in prison.

“Doctors are trained to treat patients, not to be detectives,” says Dr. James N. Campbell, a Johns Hopkins University neurosurgeon specializing in pain, who will be another witness for Dr. Hurwitz. He says that doctors have already reacted to the D.E.A. crackdown by changing the way they deal with the many Americans -- at least 50 million, by several estimates -- who suffer from chronic pain.

“Opioids were a revolution in pain treatment during the 1990s, but doctors are now more reluctant to use them,” Dr. Campbell says. “If a doctor perceives there's a 1 in 5,000 chance that a prescription will lead to a D.E.A. inquiry -- just an inquiry, not even an arrest -- he's not going to take the chance. So the victims are the patients.”

New York Times