The active ingredient in d-CON rat bait pellets is brodifacoum, the same active ingredient in the company's mouse bait pellets, wedge baits and place packs. The active ingredient in its bait stations is diphacinone. Both these ingredients are anticoagulants and rat poison manufacturers typically mix them with grains to attract the rodents.
Anticoagulants prevent the blood from clotting and kill rats and other rodents over several days from ingesting the bait. Some of the poisons require that the pests have access to the bait regularly for up to 15 days while others are lethal with a single dose. Preventing blood clotting causes the pest to die of internal bleeding. The time between ingesting the bait and the animal feeling its effects prevents rats from avoiding eating it.
The use of anticoagulants as rodent poisons first began in the 1940s. However, by 1958 pests in areas where consumers used it regularly were becoming somewhat immune to its effectiveness. The resistances lead manufacturers to develop the second generation anticoagulants, including brodifacoum. These single-feed anticoagulants are highly effective and their effects are cumulative, so animals consuming several small feedings also die.
Rat poisons have similar effects on all mammals and misuse of them can cause death of pets, including cats and dogs. The anticoagulant may also affect scavengers consuming rodents that die from it.