H1 antihistamines are a class of medications primarily used to relieve allergy symptoms, such as sneezing, runny nose, and itching. They work by blocking the action of histamine, a substance in the body that causes allergic reactions. Common examples include diphenhydramine and loratadine. These medications are often available over-the-counter and can be taken in various forms, including tablets, liquids, and nasal sprays. While effective for allergies, some H1 antihistamines may cause drowsiness, so it's important to read labels and consult with a healthcare provider if you have concerns about their use.