Hi. I have two 7 month old kittens that I introduced to my 11.5 year old. We used plug ins for three months and they didn't have any side effects any of my cats. The older one just occasionally tried to rub on the plug ins. We also use the spray for the crate/vet trips and it works well. You might want to call the manufacturers, but I love these plug ins. they didn't even have an effect on our asthma-we'd use them again in a minute, in fact we're moving in february and will use them then. Take care and good luck,

Lisa S.

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