No product made for dogs is safe for cats. Many products like pyrethrums (natural but deadly) are fine for dogs but deadly for cats. Call the vet - product in hand - and read the ingredients off to them and they will tell you what the risk is. In the meantime any symptoms at all - lethargy, hiding, circling, tremors, pupils unequal in size, or confusion - means you go to the emergency vet NOW. Note that "natural" is not the same as safe. Many "natural" products are much more deadly than the ones that your vet has. Pyrethrums are a prime example - derived from the chrysanthemum plant, it is totally natural but deadly to cats. Eucalyptus is another one.