Nell asked about the proper dosage of Revolution for ferrets, and about possible adverse side effects of over-dosing. I'll share my own experience, and what I know from my past researching, about both questions. Revolution will kill pretty much all parasites by getting into the ferret's bloodstream and thus into the parasite's food supply. Here is a link to the Revolution website with info about the product for cats, which is what we use for ferrets: https://www.revolution4cats.com/default.aspx?sec=Product%20Overview The main reason that I and many others use Revolution is for heartworm prevention. Heartworm can be spread by mosquitos, so I only use Revolution for my ferrets during mosquito season, which, here in CT, is basically April -- September. IF you want proper heartworm prevention, then my belief is that 18 mg of selamectin, the active ingredient in Revolution, given once per month, is adequate for protection for a ferret of roughly 2 lbs. or slightly more (1 kg). I do have a study that was done for many animals, including ferrets, on selamectin, and that is where the 18 mg per month number comes from. I can email it to anyone who would like a copy, so just write to me privately. The small vials of Revolution, for cats up to 5 lbs., contains 15 mg of selemectin, which I don't feel is enough to safely guard against heartworm, especially since my ferrets are almost always over 2 lbs. in weight, and often the boys are upwards of 3 lbs. The larger vials of Revolution, for cats 5-15 lbs., contain 45 mg of selamectin. SO, I use 1/2 of that sized vial once per month per ferret during mosquito season. That delivers approximately 22 mg. of selamectin per ferret per month. I have never had any kind of adverse reaction at all to that dosage by any ferret. As for 'over dosing', I used to give my ferrets a WHOLE vial of the larger cat-sized Revolution, or 45 mg of selemectin per month. This was before doing more research on my own and coming to the conclusion that I feel more comfortable with now. So, they were getting 45 mg of selemectin monthly during mosquito season. Fortunately, I never saw any adverse reactions at all to that size dosage, either. And, if you read back on some of the archives in the Ferret Health List, you will see that some vets, at least in the past, recommended the whole tube of the cats sized 5-15 lbs. per ferret per month. SO, I don't think you can really overdose on Revolution unless your ferret is small and/or you really give him or her an awful lot of the stuff. However, with that being said, I also don't see any reason to take that chance IF you believe that 1/2 of a vial of the cat sized 5-15 lbs. is adequate to offer the protection you're seeking for your ferrets. And, given the current cost of Revolution, which seems to go up quite a bit every year, there's another reason not to over-medicate with it. Jeff In Loving Memory of Neo, Trinity, Morphy, Dozer, Possum, Pip, Pop, Sabrina, Minnie Mouse, Hunny, Misty, Frodo, Baggins, and Mr. Parker Caring for Luna, Baby Girl, Boomer, and Zoomer [Posted in FML 7301]