April 25 (HealthDay News) -- The U.S. Food and Drug Administration has approved Relistor (methylnaltrexone bromide) to treat constipation stemming from continuous use of opioid painkillers.

Opioids, including morphine, are commonly prescribed for people with late-stage cancer, heart failure, respiratory disease and other illnesses. But the painkillers can interfere with normal bowel function by relaxing the intestinal muscles that push out waste.

Relistor prevents opioids from affecting these muscles, allowing the bowels to function normally.

The drug is injected at intervals not to exceed once in 24 hours. It's not recommended for people with known or possible bowel obstructions. Side effects can include abdominal pain, gas, nausea, dizziness and diarrhea. Users with severe symptoms should discontinue the drug's use, the FDA said.

Relistor is produced by Philadelphia-based Wyeth Pharmaceuticals and Tarrytown, N.Y.-based Progenics Pharmaceuticals.