Genes May Influence Reactions to Painkillers

WEDNESDAY, June 20 (HealthDay News) -- Genetics play a major role in a person's risk for addiction or unpleasant side effects when taking opioid painkillers, new research suggests.

Opioids, also called narcotics, are commonly prescribed to treat moderate to severe pain and include drugs such as morphine, methadone and oxycodone.

Some people experience debilitating side effects when taking opioids, while others have no problems. Similarly, some people can take these medications for months with little chance of addiction, while others are at risk within weeks.

To examine these patient differences, researchers from the Stanford University School of Medicine assessed the responses of more than 120 twin pairs and non-related people who were given the opioid alfentanil, a short-acting painkiller prescribed by anesthesiologists.

One finding of the study was that identical twins were more similar in their responses to the drug than non-identical twins, which suggests that genetics are a major factor.

Specifically, the researchers concluded that genetics play a significant role in a patients' variability for the risk of opioid side effects. They accounted for 59 percent of the variability for nausea, 38 percent of itchiness, 32 percent of dizziness and 30 percent of slowed breathing.

In addition, genetics accounted for 36 percent of drug disliking and 26 percent of drug liking, which are measures of addiction risk, according to the study published online June 20 in the journal Anesthesiology.

"The study is a significant step forward in efforts to understand the basis of individual variability in response to opioids, and to eventually personalize opioid treatment plans for patients," Dr. Martin Angst, one of the two principal investigators, said in a Stanford news release.

"Our findings strongly encourage the use of downstream molecular genetics to identify patients who are more likely or less likely to benefit from these drugs -- to help make decisions on how aggressive you want to be with treatment, how carefully you monitor patients and whether certain patients are suitable candidates for prolonged treatment," said Angst, a professor of anesthesia and director of the Stanford Human Pain Research Laboratory.

Earlier this year, the same team of researchers published a study that found that genetics account for 60 percent of the variability in the effectiveness of opioids in relieving pain.