Antihistamine-1 is primarily used to alleviate symptoms associated with allergic reactions, such as sneezing, itching, runny nose, and watery eyes. It works by blocking the action of histamine, a substance in the body that causes these symptoms. This makes it effective in treating conditions like hay fever, hives, and other allergic skin reactions. Additionally, it is often included in over-the-counter cold and flu medications to help manage nasal congestion and other related symptoms. In some cases, it is also used to prevent motion sickness and to induce sleep due to its sedative properties. Its application is common in both human and veterinary medicine for managing allergic responses in animals.