BUFFALO, N.Y. (WIVB) — Another study is showing the ugly side of opioids.

We know they are addictive, which can be deadly, and doctors have questioned how well they actually relieve pain before. Now, they have evidence that these drugs can make chronic pain worse.

The study came out this week and supports all the changes the CDC has made to opioid prescription guidelines.

Only five days of morphine treatment made chronic pain worse for the rats in this study. That effect persisted for several months.

Previous studies have only looked at the short term effects, so this is especially significant.

Professor Peter Grace is the lead author on the study. He says “We are showing for the first time that even a brief exposure to opioids can have long-term negative effects on pain.”

Something in the drug activates signaline from a protein in the brain that leads the nerve cells in the brain and spinal cords to become overactive, increasing pain and making it last longer.

Doctors call it a very ugly side to opioids that had not been recognized before.

The study, which is in Proceedings of the National Academy of Sciences, can be read here.