Heartworm prevention for dogs without vet prescription is a subject of concern for many pet owners in the United States. Most heartworm prevention medications are classified as prescription-only due to the serious health risks associated with improper use. These products contain active ingredients that require accurate dosing based on a dog’s weight, age, and medical history. Administering heartworm prevention without veterinary oversight may result in ineffective treatment or adverse side effects. In the U.S., federal regulations require a veterinarian’s prescription to ensure safe and appropriate use. Skipping a vet consultation can compromise a dog’s health and long-term protection.