A prescription painkiller sold under such names as Darvon and Darvocet is too risky to stay on the market, a consumer advocacy group argued Thursday in suing the Food and Drug Administration.

Public Citizen petitioned the FDA two years ago seeking a ban on the drug, calling it no more effective than safer painkillers and citing the accidental deaths of more than 2,000 people since 1981.

Thursday, Public Citizen filed suit in U.S. District Court in Washington arguing that FDA has violated the law by not ruling on its petition within the required six months.

At issue is a narcotic known chemically as propoxyphene, sold by numerous generic manufacturers as well as under the brand names Darvon and Darvocet.

It is considered a relatively weak painkiller. Public Citizen's Dr. Sidney Wolfe cited a recent review of research studies that found ibuprofen worked better for most kinds of pain.

Yet propoxyphene is addictive, and even when used properly it can cause slowed heartbeat and other serious cardiac side effects, the lawsuit says. In addition, Wolfe said it has been deemed inappropriate for the elderly because of other side effects, include sedation and confusion, that increase risk of falls and fractures.

British health authorities ordered the drug phased out there in 2005, saying at the time that it was associated with a few hundred accidental deaths and suicides a year.

In the U.S., propoxyphene remains one of the most widely prescribed generic drugs, with 22 million prescriptions filled last year.

Neither FDA nor one of the drug's main manufacturers immediately responded to requests for comment.