Can claritin (loratadine) non-drowsy antihistamine still cause drowsiness?

Yes: Claritin is a second generation antihistamine which causes much less drowsiness than first generation antihistamine, like benadryl (diphenhydramine). The number of people who feel drowsy on Claritin is so low that it is labeled "non-drowsy". But each of us is unique. I have plenty of patients who feel drowsy on claritin, especially petite women.

Yes: Claritin (loratadine) is considered "non-sedating" in doses of 10 mg or less per day. At doses higher than that, which have been used in europe, sedation can occur. That being said, even at low doses, some patients can have paradoxical sedation, but it is not common.