The Food and Drug Administration warned that the painkiller codeine, if taken by certain nursing mothers, could potentially pose a risk of overdose to their infants. Doctors treating nursing mothers should prescribe low doses of codeine. Mothers taking codeine should be attentive to signs of excessive sleepiness or limpness in their babies. The FDA will also ask makers of codeine-containing products to put information about the risk into their labels. In particular, infants of women whose bodies process, or metabolize, the drug very quickly may have an increased risk of an overdose, the FDA said. To determine whether a mother is a rapid metabolizer of codeine, a genetic test can be performed.