CHICAGO - There's an open secret in medicine: Patients lie.

They lie about how much they smoke and whether they're taking their medicine. They understate how much they drink and overstate how much they exercise. They feign symptoms to get appointments quicker and ask doctors to hide the truth from insurance companies.

“Doctors have a rule of thumb. Whatever the patient says they're drinking, multiply it by three,” said Dr. Bruce Rowe, a family doctor in suburban Milwaukee. “If they say two drinks a day, assume they have six.”

Hippocrates, the father of medicine, is said to have warned his students around 400 B.C. that patients often dissemble when they say they've taken their medicine. TV's fictional Dr. Gregory House repeats the same message to his crack team: “Everybody lies.”

But lying can lead to expensive diagnostic procedures and unneeded referrals to specialists. It also can have disastrous results.

“I definitely learned my lesson. I could have ended up in a coma,” said Michael Levine, a 28-year-old financial adviser in Los Angeles, who lied to a specialist he saw for a wrist injury. Misguided pride, he said, kept him from mentioning the Xanax he was taking for anxiety. He didn't think the doctor needed to know.

“He wasn't my regular doctor. He was treating my wrist,” Levine explained.

The doctor prescribed the pain reliever Vicodin and Levine took it on top of Xanax. The next few days vanished in a cloud of grogginess. Levine slept through ringing phones and alarms and woke up exhausted. His wrist pain was easing, but he could barely function. Eventually, he stopped the Vicodin, returned to the doctor and, under questioning, confessed.

“The doctor said, ‘Why didn't you tell me? I never would have prescribed you that,”' said Levine, who now realizes how easily he could have overdosed and died. “For the future, I will always 'fess up.”

Why do patients lie? The examination room itself is an environment that discourages honesty, said Los Angeles psychiatrist Dr. Charles Sophy.

“You're naked in a gown and you have a guy standing there clothed, with a coat on and there's all sorts of things in his pocket. And you're sitting there, basically naked ... that makes it hard to come clean,” Sophy said.

On top of that, the doctor may be rushed.

Researchers say patients often lie to save face. They want to be “good patients” in their doctors' eyes. But that's a misguided and risky practice. For example, a woman who doesn't want to admit she smokes and then is prescribed birth control pills is at greater risk for blood clots.

Some researchers estimate more than half of patients tell their doctors they're taking their medicine exactly as prescribed when they're not.

A study by researchers at Johns Hopkins School of Medicine found a big gap between what patients said and what they did. Researchers looked at how patients with breathing problems used an inhaler equipped with a device that recorded the date and time of use and compared that with what the patients said.

Seventy-three percent of patients reported using the inhaler on average three times a day, but only 15 percent actually were using it that often. And 14 percent apparently deliberately emptied their inhalers before their appointments to make it look as if they were good patients.

Some doctors are seeking approaches that encourage more honesty. Dr. Zach Rosen asks his patients a series of questions to determine whether they're taking their medicine.

“I ask, ‘What medications are you taking?' At first, I just want the names,” he said. “They say, ‘I'm taking X, Y or Z.' Then I'll say, ‘That's great. How often are you taking that medication?' ... Then I'll say, ‘Are you experiencing any problem in taking your medications?”'

Asking several questions takes more time. But the approach elicits better, more honest responses, Rosen believes.

When alcoholics seek detox treatment from Dr. Akikur Mohammad, an addiction specialist at the University of Southern California School of Medicine, they must tell him exactly how much they've been drinking.

“I tell them, ‘You can lie to your friend, you can lie to your family members, but you came here for help and your report will determine the treatment plan. If I undermedicate you, you may have seizures and die,'” Mohammad said. Despite the warnings, patients still sometimes mislead him, he said.

Cyndi Smith, a 45-year-old Weight Watchers leader in suburban Chicago, admits her own lying past. She says she lied because she was fooling herself.

“You convince yourself of certain things and it becomes true, when in reality it's not,” she said. If her doctor had questioned her more thoroughly, she says she might have told the truth.

“I think doctors could be a little more point-blank,” she said. “And we need to be a little more honest.”