This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
[{'content': 'Which of the following drug causes least sedation? \nSelect and explain. \nA. Hydroxazine, B. Phenergan, C. Chlopheneramine, D. Loratidine', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Loratadine is a second-generation tricyclic H1 histamine antagonist which acts as a selective inverse agonist of peripheral histamine H1-receptors. As a "non-sedating" antihistamine, loratadine causes less sedation and psychomotor retardation than the older antihistamines because it penetrates the blood brain barrier to a smaller extent. Other possible side-effects include headache and antimuscarinic effects such as urinary retention, dry mouth, blurred vision, and gastrointestinal disturbances.', 'role': 'assistant'}]