All web pages I went to said that capstar is safe for cats to get rid of fleas. So I went and bought a pill for each of my six cats. Within 15 minutes giving the pill, two cats ran around screaming bloody murder. So I took them into the bathroom and just kept using the flea comb. I then go to check the other cats and one cat is panting real bad. It was very hot and humid so I brought him into an air conditioning room. I then started to read the pamphlet of capstar but lo and behold, no info on adverse effects, in fact really no info. So I call the pet store where I bought it and she said she never heard anything like that and not to worry. While I'm on the phone, this cat disappears. So I start looking for the other cats and I find another cat panting real bad. I bring her in the air conditioned room and she is running back and forth panting. So I try looking online for capstar for adverse effects and finally find something that states some cats do start panting, vocalizing, vomiting, etc. So I call the 24 hour vet and they said if she is still panting in 20 minutes to bring her in. So after 20 minutes, still panting and running around like crazy, I bring her to the vet. I still never found the other cat who was panting. So anyway, I get minnie to the vet and they immediately take her to give her oxygen. After about 1/2 hour vet says minnie stopped panting. They took her temp and she was normal. So he told me to call poison hotline which I did but they wanted $65 and then told me they could not help me because I did not know the dose. In the meantime, my son calls me and tells me he found the missing cat who was panting and he seemed fine so I told vet I just wanted to take minnie home to monitor her. So after $200, waiting around for 2 hours at the vet, everything seems fine now. I'm really just wanting to warn people who are thinking of using capstar. There are sometimes adverse affects. If you are thinking of using it, use it when you can monitor the cat, do it during the hours when you vet is around (today is sunday so I had to pay alot), and don't do it when it is hot and humid. I used it on six cats and four had adverse effects, and it was the correct dose because I weighed each cat this week. I know I rambled but I just don't want someone else to go through what I did.