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
Effects mediated by H1 histamine receptor include: 
Select and explain. 
A. Inhibition of gastric acid secretion, B. Induction of hepatic cytochrome P450 enzymes, C. Maintenance of a wakeful state, D. Vasoconstriction of arterioles
C: Maintenance of a wakeful state
Answer: C: Maintenance of a wakeful state 
Explanation: Sedation occurs with those drugs that are potent antagonists of the H1-histamine receptor, including chlorpromazine, olanzapine, quetiapine and clozapine.
Histamine H1 receptors mediate many pathological processes, including allergic rhinitis, atopic dermatitis, conjunctivitis, urticaria, bronchoconstriction, asthma and anaphylaxis. Moreover, histamine stimulates the parietal cells in the stomach, causing an increase in acid secretion via the activation of H2 receptors.​
Reference: Lippincott Illustrated Reviews: Pharmacology Wolters Kluwer Sixth Edition page no 150,394​