Milbemax is what barney was given the very first time we went to see our vet. She gave him a small puppy dose - meant to be monthly until 6 months and then once every three months after that i think. Barney had no side effects at all. We forgot to give him some recently so we'll be going along to teh vet tomorrow morning to get some and get him weighed to make sure its teh right dose - its so difficult to remember to give these things at the right time!