BUFFALO, N.Y. -- A new study is putting some stark numbers on the opioid crisis.

The National Institute on Drug Abuse found that in 2015, 92 million U.S. adults, more than one-third of the American adult population, used some form of prescription painkillers.

The study also found that 11 million said they'd taken them without doctor's orders, or had received them from family or friends.

Doctor Kenneth Leonard from the University at Buffalo Research Institute on Addictions joined 2 On Your Side Monday to discuss the study.

When asked if the results surprised him, he responded: "We've all known for some time that there's been a problem with opiates and there's been this increase in the number of opiate prescriptions. But the sheer number of people who are receiving prescriptions in 2015, which this study is based on, was staggering and very surprising."

When 2 On Your Side asked about why these numbers are so high, Leonard responded: "The report that came out today talked about the reasons people misused. Misuse was about 12 percent of the people who had a prescription for opiates and among those people who misused, many of them misused for the same reason they were prescribed it, that is they were prescribed for pain and they misused it for pain at least one time in the past year."

He also said the medications are ideal for short-term pain, but there can be issues with using them to treat long-term pain.

"There are many people who are on them for long-term pain," he said. "They have problems long-term in terms of being able to eventually coming off of them. And when people come off of them, after a long period of time, they often develop extra an sensitivity to pain."