What is in claritin (loratadine) to make you hyper?

Antihistamine : It is not common but children and adults are known to become hyper rather than sedated from 1st & even 2nd generation histamine blockers like claritin (loratadine). If it is Claritin (loratadine) alone, not Claritin (loratadine) d ( lots of decongestant), this is considered an idiopathic reaction. Meaning that your metabolism break Claritin (loratadine) down in a way that causes agitation, a stimulant.

Rarely, but it can..: Antihistamines make people sleepy/groggy and Loratadine is actually classified as nonsedating. Rare, it can cause hyperactivity, especially in children; we don't know why it does that. Claritin-d which is in combo with a decongestant Pseudoephedrine which can cause hyperactivities/jitteriness/rapid heart rate etc. Consut doc if you hve trouble. Good luck.