[bigheadfred]

Used to be the main ingredient in rat poison was Warfarin.

Same thing ya’ll get can from your doctor.

Got some in my medicine cabinet.

[SunkenCiv]

Not too sure that isn’t still in use.

I’ve got some ideas about how to rid cities of rats, and NYC would be a great place to start working on it, with its billion-ish rat population.

And ahead of time, I’d be preparing a huge breeding population of voles (North America’s native relative of the hamster and lemming) to fill the niche vacated by the rats, to keep them from regaining a foothold.

[CedarDave]

It's the same thing as the products listed in my opening excerpted sentence. Here is the entire paragraph which I had to cut to meet the posting limitations:

Known as anti-coagulants, the chemicals prevent blood from clotting or coagulating. One is known as warfarin — the same chemical sold to people as Coumadin, a prescription blood thinner. A new "super toxic" strain of rodenticide was developed in the 1970s because it required only a single dose to kill a rat. The Brand names include Havoc, Talon, Contrac, Maki, Ratimus and d-CON Mouse Pruf II.