Robert , what you described in 3 experiences is what we in the drug manufacturing industry call Adverse Medical Events. Loss of effectiveness , allergic reactions, and complete loss of hair beyond what is listed in the package insert are all potentially caused by drug that was counterfeit - a huge problem, especially when buying mailorder from resellers from outside US Borders who do not have chain of custody integrity. Also the active indregiant may have degraded if stored outside the validated stability conditions (it was frozen in the back of a loading truck, or overheated) . Last it may be cuased by a bad batch. While the regs for making of veternary drugs are less burdensome to meet than for human drugs (process validation is not required) manufacturers are required to investigate any consumer complaint. Would you please use the FDA Adverse Event reporting page and report all three events? You will eventually get back a letter from the manufacturer with the results of the investigation. Also the local FDA office or CDER will use the complaints in their next inspection of that manufacturing site to see if specific findings are related to other deficiencies they may find during the biannual inspection. You can make your AER here: http://www.fda.gov/Safety/MedWatch/HowToReport/ucm053074.htm Under submitting online. You will want to keep as much information as possible , such as the label with the lot number, experation and NDC number to enter on the site. I also use Revolution. I have not had these issues but I have read quite a few complaints regarding other unrelated drugs at companies I have worked at and sometimes consumers can be very helpful to the manufacturer to improve product quality. As for the cat (and I am not a Vet, nor have I ever worked at the manufacturer of this product) It sounds that the slight hair loss is not unexpected. For the dog however that could be loss of potency, indicating that the dog's dose has no active ingredient left. I would stop using that box, save it and let them ask you for it , then send it in and they will test it for label claim. They will likely also give you 2 free boxes in exchange and some coupons (we would, where I used to work). As for the ferret, this is more serious potentially an overdose, and needs follow up. I would stop using that batch as well, save it and try again with another lot number from a difference source AFTER, discussing with other Vets. I would get it direct from a Vet, to minimize potentially having a batch that was stored outside expected temperature conditions, and is not coming up to expiration shortly. Check if it still has at least 6 months to expiry left. Save that questionable box (Revolution kitten dose) as well. On a side note, I am somewhat disappointed your Vet didn't do this reporting already. Michael [Posted in FML 7368]