Although toxicity levels of rodenticides may vary between target and non-target species, all poisons must be presumed to be lethal to humans. The hazard is by accidental poisoning because there is no evidence that rat poisons could enter the human food chain. Acute poisons are potentially more dangerous than chronic ones because they are rapid in action, non-specific, and generally lack effective antidotes. Anticoagulants, on the other hand, are slow and cumulative, allowing adequate time for the administration of the reliable antidote, vitamin K. The concentrations of active ingredients in contact formulations of a given poison are higher than those in bait preparations, thus making operator hazard considerably greater. Fumigants present a special danger when used to treat infested premises, holds of ships, etc, and should only be used by trained technicians. The gassing of rodent burrows, although less hazardous, must also be carried out with extreme caution.
In 2000 it was reported that about 30 percent of UK barn owls found on roadside verges ("road-kills") contained second-generation rodenticides. (In 1983 this had been only five percent.) In two percent of cases, the poisons had been directly responsible for the birds' deaths. A similar study of polecats and foxes found that about 45 percent contained rat poisons and that 10 of the 100 foxes had died from the poison. About one quarter of weasels and stoats were similarly affected.