More than half of adults and 44 percent of children who were drug-tested by a national clinical laboratory last year misused their prescription medications, according to a study released Monday by Quest Diagnostics.

Misuse of medications can mean that patients were either taking too much, too little or none of their medications. It also can mean test results showed they were using other drugs that had not been prescribed, including illicit drugs — as 45 percent of adults were doing, the study found.

“These are situations where the patient is placing their life at risk,” said Leland McClure, a director with Quest, which is the nation’s largest provider of clinical laboratory testing.

The rate of misuse identified by the study might skew higher than what would be found in the general U.S. population. Some patients were tested because their health providers determined there was a “high probability” of them mismanaging medications, the study said.

The study also identified the drugs most often misused by patients depending on their age: amphetamines for youth 17 and under, but benzodiazepines and anti-anxiety medications for adults 25 and older, followed by opioid painkillers.

The study provided regional results for adults. The highest rate of misuse, nearly 66 percent, occurred in Colorado, Montana, North Dakota, South Dakota, Utah and Wyoming. The lowest rate of misuse, about 51 percent, took place in Alabama, Florida, Georgia, Kentucky, Mississippi, North Carolina, South Carolina and Tennessee.

This fifth year of the prescription drug study made use of more than 3 million test results. The testing checked for 44 drugs in 2015, up from 26 drugs in 2010.

For the first time, the latest analysis also included 155,646 heroin test results, which showed that nearly one-third of patients tested positive for benzodiazepines. Both heroin and that group of medications lower respiratory rates. When they are combined, patients can stop breathing, have heart attacks and die, McClure said. And those combinations are happening with an “alarming magnitude,” he added.