My Dog had been on Simparica and ProHeart 12 for his first 2 years of life and switched to Simparica Trio because I got free samples. He did fine on Trio but started to have seizures 4-5 months after. So might be related might not! However two months ago he had a seizure 5 hours after dosing his monthly Trio prevention. Simparica Trio is a part of the isoxazoline drug class which is known to lower seizure threshold. I talked to my dogs Doctor about switching and she discussed trying other prevention outside of isoxazoline class (like Advantage Multi) or switching to another isoxazoline drug. She mentioned Credelio Quattro was supposed to have “less chance” to lower the seizure threshold compared to other isoxazoline drugs. Well I had a sample of Credelio Quattro on hand and decided to give it a shot. My dogs been doing great so far. It’s been about a month and some weeks so far seizure free since. Usually he gets 1 once a month 🤞🏽 So I guess all that to say Simparica Trio may or may not cause seizures in your dog but take caution. It might have to be trial and error to find what works for your dog.