Another commonly claimed rat repellent is ammonia. This nitrogen-based compound is a common killer of aquarium fish and amphibians, and similar to naphthalene reduces the blood cell’s ability to carry oxygen. Is this any better?

Unfortunately, it’s not. The reason ammonia can commonly lead to the deaths of fish is that they’re trapped in small aquariums and may not have their water changed. Therefore, the ammonia builds up and builds up until there’s so much of it that it kills these creatures. When it comes to rats, there’s just no way to expose them to enough ammonia for it to be harmful, especially when they have a whole house to move about in. In fact, all living things produce ammonia naturally, and rats are known for having plenty of it in their urine. So adding a bit more ammonia here and there really doesn’t accomplish anything.