Hismanal, a prescription antihistamine whose sales have steadily dropped in the wake of warnings about serious side effects, is being pulled off the market, the manufacturer announced yesterday.

Janssen Pharmaceutica said the decision to stop selling Hismanal was a voluntary business decision, calling the allergy marketplace too crowded.

The decision is not a recall -- Hismanal supplies left on store shelves will continue to sell until supplies are gone, said Janssen spokesman Greg Panico.

"We would advise patients who currently are taking Hismanal to consult their physicians about treatment alternatives," he said.

Hismanal sales have dropped in recent years after repeated warnings from the Food and Drug Administration that the hay fever and hives medicine can cause potentially deadly side effects when taken with other drugs -- and even when taken with grapefruit juice.

Early last year, when the FDA issued strong new warnings about Hismanal's risks, the drug accounted for just 3 percent of the antihistamine market. Still, that accounted for some 1 million prescriptions. Janssen did not release updated figures yesterday, but experts say sales have continued to drop.

The FDA did continue to receive scattered reports of side effects suffered by people who either had not heard the warnings or had not heeded them. Some critics had wondered why Hismanal continued to sell when the competing antihistamine Seldane was pulled off the market last year for similar side effects.

In the Seldane case, the FDA had approved a safer substitute -- the same chemical, revamped to be safer. There was no safer substitute for Hismanal, said the FDA's John Jenkins.

Still, "we clearly were continuing to evaluate the safety of Hismanal and continued to have concerns," Jenkins said. "We certainly support Janssen's voluntary decision to stop marketing."