Hartz flea medicine is the worst flea and tick preventative medicine I have ever used. I would never recommend this product to anyone. We used it one summer on our 3 dogs because we were low on money and thought we would try Hartz to see the difference between it and Frontline. Our dogs became infested with fleas! It was horrible. I've never had fleas or ticks on them at all before and they were suddenly covered in them. It was like using water, it didn't do anything. It is very cheap medicine and it shows. I went back to Frontline and will never switch again.