An antihistamine is a type of pharmaceutical drug that opposes the activity of histamine receptors in the body.Antihistamines are subclassified according to the histamine receptor that they act upon: the two largest classes of antihistamines are H1-antihistamines and H2-antihistamines.n H3-antihistamine is a classification of drugs used to inhibit the action of histamine at the H3 receptor. H 3 receptors are primarily found in the brain and are inhibitory autoreceptors located on histaminergic nerve terminals, which modulate the release of histamine.
U.S. Secret Service. U.S. Secret Service, federal law-enforcement agency within the United States Department of Homeland Security tasked with the criminal investigation of counterfeiting and other financial crimes. After the assassination of Pres.
The National Security Agency is a highly specialized and vital unit of the American intelligence community that works to create and break secret codes, a science known as cryptology. The National Security Agency, or NSA, reports to the U.S. Department of Defense. The work of the National Security Agency is done in secret and in the name of national security. The government did not even acknowledge the NSA existed for some time. The National Security Agency's nickname is No Such Agency..