From the Manufacturer:
Hartz First Defense Topical Remedy for Cats 3 lbs or more kills Fleas, Ticks, and Chewing Lice in addition to prevents and controls re-infestations. Rapid acting, long lasting, water-proof formulation is still effective even after bathing, water immersion, or exposure to light.
** These statements have now not been evaluated by the Food and Drug Administration. These merchandise don’t seem to be meant to diagnose, treat, cure or save you any disease.