CHICAGO (AP) – There’s an open secret in medicine: Patients lie.

They lie about how much they smoke and whether they’re taking their medicine. They minimize 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 and convey that by the way he or she asks questions.

Researchers say patients often lie to save face. They want to be “good patients” in their doctors’ eyes. Some researchers estimate more than half of patients tell their doctors they’re taking their medicine exactly as prescribed when they’re not. In reality, they don’t like the side effects, can’t afford the pills or didn’t understand the instructions.

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 used an inhaler equipped with a device that recorded the date and time of each use and compared the actual recorded use 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 like they were good patients.

Cyndi Smith, a 45-year-old Weight Watchers leader in the north suburbs of Chicago, said before she joined the group she lied to her doctor about exercise and nutrition. She lied because she was fooling herself, she said.

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

Doctors also should avoid phrases that sound judgmental, said Nate Rickles, an assistant professor of pharmacy at Northeastern University. There’s a big difference between “Why aren’t you taking the medication as prescribed?” and “A number of my patients don’t take their medication as prescribed and they do it for a variety of reasons. What do you think might be going on with you?”

Leaving out information, not exactly a lie, can happen when doctors don’t ask the right questions.

A survey of 131 gay, lesbian and bisexual teenagers attending a youth conference in Los Angeles found that only 35 percent had told their doctors their sexual orientation. The findings were published in December’s Archives of Pediatrics & Adolescent Medicine.

“This is a very open group ... open enough to come to a conference for gay youth,” said RAND researcher and UCLA pediatrician Dr. Mark Schuster, a co-author of the study. “[Paticents] would be happy to be open with their physician, if the physician would ask.”

In fact, 64 percent, when asked what their doctor could do to make them comfortable with disclosing their orientation, marked the choice on the survey, “Just ask me.”