Some flea and tick medications take quite a long time to become effective, but others can bring your dog or cat relief within just a couple of hours! The revolution begins working almost immediately. Splitting Vials Risk Minimising Dr Matt Allworth Veterinarian Bayer Products Flea Treatment Saving Money Chart Then it should last a full month after that. How long does revolution flea medicine take to work . Unlike numerous parasites, most fleas reside in the environment, not on your animal. Nothing can stay forever and ever, including the lives of us humans. Some are even effective for eight to twelve weeks! So yes, flea and tick treatments have expiry dates. How long does it take for revolution for cats to work? The majority of flea products eliminate adult fleas and stop them laying eggs, but none work immediately. Revolution will start to kill and repel fleas from your cat or kitten within half an hour and then within 24 hours should be in full cycle. It should ...