Morphine tolerance - or patients getting used to the pain-relieving effects of the drug, leading to escalating dosage - could soon be a thing of the past.
Researchers at the Saint Louis University of Medicine have found a way of blocking a key substance that causes tolerance levels to rise.
The study could lead to new therapies that allow morphine to be administered without patients developing tolerance or experiencing a host of severe side effects that accompany increasing dosage.
Findings of the study have been published in this month's Journal of Clinical Investigation.
"We believe these findings represent a major breakthrough in understanding how tolerance to the pain-relieving action of morphine and other opiate medications develops and how it can be prevented from happening in the first place," said Daniela Salvemini, the study's lead author.
Morphine is one of the most powerful treatments for severe pain, but its effectiveness lessens significantly with repeated doses.
As tolerance develops, increased doses are necessary for equivalent relief, but this also causes a variety of complications, including over sedation, respiratory problems and the potential for addiction.
Using an animal model, the researchers found that a substance called peroxynitrite plays a critical role in the development of morphine tolerance.
The researchers found they could prevent morphine tolerance from occurring by therapeutically manipulating peroxynitrite - in other words, preventing it from working.
"We believe our findings can be used by researchers to develop therapies that will allow patients to take morphine without becoming tolerant of its benefits," said Salvemini.