Final answer:
H₁-antihistamines are the drugs used for blocking H1 histamine receptors of C neurons. They prevent histamines from stimulating itching and swelling of body tissues.
Step-by-step explanation:
The drug used for blocking H1 histamine receptors of C neurons is H₁-antihistamines. Antihistamines work by binding to histamine H₁ receptors in mast cells, smooth muscle, and endothelium in the body, preventing histamines from stimulating the itching and swelling of body tissues. These drugs are commonly used to treat allergic reactions in the nose, such as itching, runny nose, and sneezing, as well as insomnia, motion sickness, and vertigo caused by problems with the inner ear.