Most commercial rat poisons contain anticoagulant drugs such as warfarin, diphacinone or bromadiolone. Alternative rat poisons may contain vitamin D, bromethalin, strychnine or zinc phosphide.
While they are popular rat poisons, warfarin and other anticoagulant drugs are safe, effective medicines used to treat ischemic stroke, deep vein thrombosis and other human disorders caused by blood clots. Anticoagulant rat poisons are safer to use around children and pets than other varieties because antidotes for these poisons are readily available and effective.
Zinc phosphide and related metal phosphide compounds are fast-acting rat poisons that produce toxic gas in the rat's digestive system. Zinc phosphide is used in bait traps while other metal phosphides are reserved for fumigation. While historically popular, zinc phosphide has been supplanted by the anticoagulants as the most common rat poison on the market.
Vitamin D kills rats by disrupting the balance calcium in the body. Vitamin D and anticoagulants are synergistic, meaning that a mixture of the two is more toxic than either one alone. As a result, anticoagulants are often added to rat poisons that contain Vitamin D. Vitamin D is less toxic than older poisons such as strychnine or zinc phosphide to children and birds, but poses a danger to dogs and cats that consume poisoned rat bait.