Captar Green Flea Control Pill Kills Fleas on Dogs Over 25 Lbs. Kills 90% of adult fleas on dog within 4 hrs. Starts working in 30 minutes. You may see your dog scatch during this time. This is due to the fleas dying, not the meds. Contains 57.0 mg. of nitenpyram. Not for human use. Keep out of reach of children. Use smaller blue pill for cats. Treat all pets in the home. Treat home, yard and car to prevent reinfestation. May be used with flea shampoo, dip and spot on treatments. May be used up to once a day. Pet must be over 2 lbs. and over 4 weeks of age to use Capstar. Green pill for dogs over 25 lbs. One tablet.