He has never had a seizure before and he wasnt sick and was taking no other medication. I am just wondering whether this seizure occured because of Zyrtec. It does state under 'side-effects' that seizures can occur. If this is the case, does the seizure occur soon after taking the first tablet or can there be a delayed reaction, that is, a seizure occurs 2 weeks after commencing the tablets. Can someone help please?