It's just about that time of year here and I have to start thinking about fleas, ticks, and heartworms. I have been reluctant to give Tucker flea and tick stuff because he had an adverse reaction to flea stuff we gave him a couple of summers ago when he got fleas. It wasn't terrible or anything, but he went off his food for three days and became lethargic. Other than that he's never gotten the preventative. But tick diseases terrify me. So I think I might give him something this summer. I also worry about giving him something that could hurt the cats. So, what preventatives do you use on your dogs or have you used in the past? How well did/do they work? Has your dog ever had an adverse reaction to it?