California will require aspirin makers to warn women against taking the drug in the late stages of pregnancy, a state science panel has decided. The panel on Friday classified aspirin a ``reproductive toxin'' under Proposition 65, the landmark toxics initiative law that requires public warnings for substances that pose a risk of cancer or birth defects. The warnings _ probably on aspirin labels _ must appear within one year after a substance is formally listed in keeping with the panel's decision. In making its recommendation, the panel rejected a $500,000 report prepared by the aspirin industry. That report said it found no evidence that aspirin taken in the last three months of pregnancy could cause excessive bleeding during delivery and other pregnancy complications. The panel unanimously ruled that such risks have been shown, based on studies involving high aspirin dosage. But panel members also acknowledged recent studies that aspirin in very low doses _ half a tablet or less _ may relieve certain medical problems suffered by pregnant women. They said the aspirin warning should be qualified to advise women against taking aspirin in the last three months of pregnancy ``... unless directed to do so by your doctor.'' Aspirin products have carried a general warning label since 1982 and certain over-the-counter aspirin substitutes also carry a label that reads: ``It is especially important not to use aspirin during the last three months of pregnancy unless specifically directed to do so by your doctor because it may cause problems in the unborn child or complications during delivery.'' Proposition 65 mandates public warnings but does not dictate warning labels on specific products. However, a spokesman for the aspirin industry said a warning label seemed likely in about a year. The U.S. Food and Drug Administration notified state authorities last week that it planned to require a new warning on over-the-counter aspirin products similar to the warning under review by the Proposition 65 panel. But science panel members said they saw no point in waiting for federal action. Aspirin industry representatives said the FDA was pushed into action by Proposition 65, which has served as a model for toxics legislation across the country.