Public Citizen, a consumer advocacy group, has petitioned the Food and Drug Administration to give generic companies greater control over their labels, a rule change that could allow users of generic drugs to sue, but the agency said earlier this month that it needed more time to decide. “Congress can make this problem go away, and the F.D.A. could, too,” said Allison Zieve, the director of Public Citizen Litigation Group. “But we haven’t seen signs that either of them is paying much attention.” A spokeswoman for the F.D.A. declined to comment.

The Supreme Court’s ruling, which was split 5 to 4 on ideological lines, has its roots in the Hatch-Waxman Act, the 1984 law that opened the floodgates to generic drugs. That law allowed companies to skip the lengthy process required to approve new drugs if they could prove that the generic drug was equivalent to its brand-name counterpart.

With few exceptions, it also required generic manufacturers to use the same labels — the lengthy list of a drug’s uses, dosages and risks — used by the brand names.

If a problem develops, the brand-name companies are responsible for changing the label, and the generic companies must follow their lead. As a result, the court’s majority ruled, generic companies cannot be held responsible for failing to alert patients to problems with their drug. The dissent, which was written by Justice Sonia Sotomayor, argued that generic companies nevertheless have a responsibility to report problems to the F.D.A. and should be held liable for failing to warn patients.

The ruling came just two years after the Supreme Court established — in Ms. Levine’s case — that, by contrast, brand-name companies can be sued for failing to adequately warn patients.

Ms. Levine was given an injection of Phenergan in 2000 during a visit to a clinic to treat a migraine headache. Her hand and forearm turned black and eventually had to be amputated. Reports had shown that the drug can cause gangrene if it enters an artery, especially if it is placed directly into the vein rather than injected into the muscle or through a diluted intravenous drip. Although the label warned that gangrene could occur if the drug came into contact with arterial blood, Levine argued that the warning did not go far enough.