Many people who undergo urology procedures may be sent home with more narcotic painkillers than they need - leaving home medicine cabinets filled with the potentially addictive drugs, a new study suggests.

Researchers found that of 213 patients prescribed narcotic painkillers after surgery for a urological condition, two-thirds had leftover pills a few weeks later. And most - 91 percent - were keeping those leftovers in their medicine cabinets.

That’s a problem, the researchers say, because those pills can be abused by anyone with access to the medicine cabinet.

Prescription painkillers like oxycodone (Oxycontin) and hydrocodone (Vicodin) are second only to marijuana as Americans’ illicit drugs of choice. A federal government survey found that in 2007, more than 5 million Americans age 12 or older said they had used a prescription narcotic for “non-medical” reasons in the past month.

Just over 56 percent said they got those pills from a family member or friend.

So leftovers from legitimate narcotic prescriptions could be an important source for people looking to abuse the drugs, according to Dr. Cory Bates, the lead researcher on the new study.

As it stands, doctors basically use guesswork to decide how much pain medication to prescribe for post-surgery recovery.

“Really, it’s pretty arbitrary,” said Bates, a urologist at the University of Utah Health Sciences Center in Salt Lake City. “Most doctors try to make an educated guess about how painful (recovery) is going to be. But it’s hard, because people perceive pain differently.”

Bates said he is now prescribing fewer pills to start. “What I’ve done is basically cut what I would normally give in half.”

Some narcotic prescriptions can be refilled, so patients who need more pain relief can get additional pills, he said.

But most patients in the current study were happy with their pain relief even though the majority did not take the entire prescription. Two to four weeks after surgery, 86 percent said they were satisfied with their pain control.

The findings, published in the Journal of Urology, are based on 275 patients who underwent a urological procedure at one of three Utah hospitals. The procedures ranged from relatively minor outpatient ones - like “shock wave” therapy to break up kidney stones - to major open surgery for prostate or kidney removal. Roughly two to four weeks afterward, the patients completed a survey either by mail or over the telephone.

Of those 275 patients, 213 said they had filled a prescription for a narcotic painkiller.

The majority - 63 percent - were prescribed hydrocodone with acetaminophen (brands like Vicodin and Lortab), while 28 percent were on oxycodone with acetaminophen (Percocet, Endocet). On average, they were prescribed 22 to 29 pills.

Overall, Bates and his colleagues found, the patients reported taking only 58 percent of the medication, and 67 percent said they had leftover pills.