Every month, more than a thousand New Yorkers grab their phones, dial 311, and cry rat. The city’s official hotline is increasingly inundated with rodent complaints—topping 31,000 in 2016.1 And if you’re going by residents’ social media accounts, the city is under siege, overrun by a bold horde of pizza-grabbing, escalator-riding, snowdrift-tunneling rodents.

Bill De Blasio is only the latest New York mayor to tackle the vermin scourge. Others have tried poisons and traps, special task forces to sniff out breeding hot spots, even a “rodent academy” to teach public employees how to be first-line responders to the Rattus norvegicus epidemic. Nothing has worked. So now, De Blasio’s administration is testing a more targeted approach to hit rats where it hurts: right in the ovaries.

That’s right, we’re talking about rodent contraception. Not with hormones, but with a compound that knocks female rats into early and permanent menopause. (It also messes with sperm, but only temporarily.) The city first ran trials of ContraPest in subway stations back in 2013 as part of an NIH grant project. And this year they’ll be testing it a few residential buildings around the city to see how effective it is indoors. If it works, it could change the way humans deal with pests of all kinds—from stray dogs and cats to deer and wild pigs.

ContraPest works by attacking oocytes, the egg precursors that every female mammal is born with. The active ingredient in the product is something called 4-vinylcyclohexene diepoxide, or VCD. It’s tongue-numbingly spicy, but totally non-toxic—except to oocytes. Specifically, it binds to a receptor that, when activated by a survival factor, keeps the egg precursor alive and healthy during a female’s baby-making years. But when VCD binds, it interferes with that signal and the oocyte dies. “The chemical destroys the eggs in their very smallest form so the animals can’t ovulate anymore,” says endocrinologist Pat Hoyer, who spent two decades figuring out the mechanism in mice and rats. No eggs, no offspring.

Hoyer’s lab at the University of Arizona used VCD to make a model for studying menopause in humans, along with associated diseases like osteoporosis and metabolic syndrome. The compound is much more representative than simply cutting the ovaries out, another popular animal model for menopause. The one drawback is that it takes longer: Ovaries fail months after a few weeks of daily VCD treatment, because some oocytes will already be available for ovulation—on the path to becoming eggs—when treatment starts.

Which is why Cheryl Dyer formulated ContraPest with a second active ingredient: triptolide. The bitter chinese herb targets any oocytes that have already been activated by hormones, preventing them from fully maturing. The one-two punch prevents female rats from ovulating with just a few nights’ worth of feeding. The chemicals also break down in the rat liver within 30 minutes, so they don’t pee or poop it out into the water supply.

The final trick was to make the stuff tasty to rats. Dyer, who co-founded the biotech SenesTech with Loretta Mayer, one of Hoyer’s post-docs, worked for 10 years to find a bait formulation that didn’t burn like the world’s hottest habanero or overwhelm with bitterness. So she coated the active ingredients to smother their flavor and added a lot of fat, salt, and sugar to make it more appealing than the smorgasbord offered by New York City’s trash bins.

Because rats do 40 percent of their feeding in the first hour they’re awake, they tend to visit the same spots over and over once they find something they like. Dyer says the trick is getting the bait to highly trafficked rodent freeways. That’s what the city is doing now—tracking tiny rat pawprints to figure out where they sleep and eat. Then they’ll start putting the liquid contraceptive out in the urban wild.

In SenesTech’s first trial a few years ago, rat populations near subway stations went down by 43 percent. And, as Dyer points out, a contraceptive solution is more resilient against population rebounds than a poison-based one. Killing off a subset of rats will just open up more shelter and food for others. And with a single mating pair capable of producing 15,000 pups in one year (when you count all their progeny's progeny), it doesn’t take long for the population to make up lost ground. Not to mention the fact that poisons don’t get broken down by rats’ livers, meaning they stay in their bodies and get ingested by other animals that eat them, including dogs and cats. “This stuff never goes away,” says Dyer. “We can do better than killing.”

The Environmental Protection Agency agrees with Dyer. Last summer the agency granted approval for use of ContraPest on brown and black rats, the most prevalent in New York, and the two species that have invaded cities on every continent save Antarctica. The company is now working on a formulation for mice, and they’ve even begun testing on feral pigs in Texas, where local management agencies have taken to shooting hog families from helicopters in an effort to contain them. The New York Department of Health said in a statement that it typically evaluates products like ContraPest for up to a year before making decisions on whether or not to use it more widely. But if it goes well, by 2018 rats might be the New Yorkers having the easiest time getting birth control.

1UPDATE 2:10 pm Eastern 04/17/17: This story has been updated to correct the number of rodent complaints reported through 311 in 2016. The story has also been updated to reflect the accurate scale of the city's pilot project.