i first used hartz flea drops on my cat about three years ago, a little while after putting on the drops he started having seizures. i quit using hartz drops and about a month later the seizures stopped. next was my dog ,i put on this new 4 in 1 and she has broken out in a rash all over her body,losing most of her hair on her tail, i quit hartz and she is clearing up now. my cat also has a hard time with hairballs,a week ago i give her hartz hairball medicine and now for the last three days she has had seizures. everything finally came together,the common denominaters is hartz !!!! all three times things only happened using hartz products this has to stop.