When Boomer was younger my vet told us to take the heart worm preventative called Worm Shield (made with ivermectin). I told her that I had read aussies were not supposed to take it. She told me "Oh any reaction to that is very rare, and is only in very large doses. Your dog will be fine". She seemed insistent on using this med. I went ahead and bought it, went home to do some research before I gave it to him After doing a bit of research I found that most ppl said what the vet told me "it's rare and only in large quantities". So I gave it to my pup. Boomer has been fine on it except for one thing. Im not quite sure if this is because of the pill... but it seems as though he gets nauseated and throws up a day or two after he takes it. I remember last month he vomited for a day after taking the pill. This month ..he threw up a couple of times yesterday, and again today. He wouldnt eat either. He does drink, however. So that was my main concern. Other than the nausea he still plays, acts normal. I've looked around the house for things he could have eaten or chewed on. I havn't found anything. One other thing i'm wondering about is that I use lemongrass essential oil (about two drops in his conditioner) for a natural flea repelant. I do that maybe once a month as well. Could either of these be causing this vomiting? I couldn't find anything about the lemongrass causing vomiting (saw a few articles saying it relieved it).