Scientists have been experimenting on laboratory, usually male, animals for decades. Female animals were avoided because their reproductive cycles would mistake the results of the experiments. The National Institutes of Health is saying that the gender unfairness with basic research needs to end. Scientists are being warned that they need to begin testing their theories in female lab animals. Women experience severe side effects and metabolize the active ingredients more slowly than men do. Some experts say that studying animals of both sexes may double the number required to produce meaningful results. The N.I.H. (National Institutes of Health) wants to direct scientists to perform their experiments with female and male animals. Officials will start the new policies in October.