Man’s best friend may live a bit longer thanks to a new pill promising to extend your pup’s lifespan

A San Francisco startup called Loyal wants to give you a few more precious moments with your loyal companion, and their results are promising.

Loyal is developing a daily prescription pill for senior dogs that the company believes can extend your loyal companion’s healthy lifespan by targeting one of aging’s most fundamental drivers: metabolic dysfunction.

“Arthritis and cancer and cognitive dysfunction are all different things,” said Dr. Brennen McKenzie, Loyal’s director of veterinary medicine, “but really, aging and metabolic health is one aspect of that that drives all these different things.”

The idea, he told Fortune, is to attack the root cause rather than play defense against each disease as it surfaces.

“If we can pick off the underlying driver for all of these things, we can have a much greater impact on health and welfare and wellbeing than just working on each individual disease as it pops up,” he said.

The drug, LOY-002, works essentially as a caloric restriction mimetic, achieving some of the same benefits as a severely reduced-calorie diet, but without the pain and suffering—or for beagle owners out there, the sheer physical strength—of refusing food to your four-legged friend.

“Part of the genius of the idea of LOY-002 is that it achieves some of the same goals biologically as caloric restriction without the hardship and the risks of doing that,” McKenzie said, referencing a landmark Purina study that found calorie-restricted dogs lived roughly two years longer on average. “It doesn’t require restricting calories, and it doesn’t cause them to lose weight.”

Loyal said the STAY study is the largest clinical trial ever conducted in veterinary medicine, which has seen an enrollment of 1,300 dogs across 72 veterinary clinics nationwide in a randomized, double-blinded, placebo-controlled design.

“We’re putting them on either the drug or a placebo, and monitoring them incredibly closely, collecting just a mountain of really interesting data,” McKenzie said. “At the end of that, we will hopefully see that the dogs on the drug are living longer, they have less frailty, they have a better quality of life, hopefully they have less age-related disease.” The study, now about two and a half years in, will run a minimum of four years.

Crucially, LOY-002 could reach the market before the STAY study concludes. Loyal is pursuing a conditional approval pathway from the FDA, a mechanism designed for exactly this kind of situation, where the drug has passed safety requirements but still needs more time to cook in the study.

“The FDA recognizes that studies like this are long. They take years and years to run,” McKenzie said. “In the meantime, there is no drug that solves this problem. There’s nothing available to try to target aging and help dogs live longer. So if we can show that it’s safe and that it’s likely to work, we can bring it to dog owners and veterinarians sooner.”

As for how many years the drug might add, McKenzie was careful: “Numbers are always tricky, because we tend to fixate on them and think they’re more reliable than they are.”

So far in the STAY study, McKenzie noted they were able to detect at least a one-year difference between the treated and placebo groups at minimum.

“I don’t think there’s any way we can say you’re going to get X number of years or months more with your dog,” McKenzie added. “I think if we can show that overall it’s more, and enough to matter, I think that’s what we’re hoping for.”

The real-world scope of the trial was itself a statement of intent.

“When we said we’re going to enroll 1,000 dogs, everybody said, ‘You’re nuts. There’s never been a study that size. It won’t happen,’” McKenzie said. In the end, over 12,000 people emailed Loyal wanting to be involved. “A lot of them say, ‘I know this may not be helpful for my dog, but the idea that I can contribute to having something that will give my future dogs and other people’s dogs more time is really motivating.’”

As for humans, McKenzie was careful to frame the drug not as a biohack or a longevity shortcut, but as something more straightforward: better preventive medicine.

“It’s not a hack. It’s not a quick trick,” he said. “It’s just taking a basic, foundational understanding of how aging and biology works, and doing better preventive medicine.”

If it works in dogs, he believes it does now give some hope for similar drugs for humans as well.

“If we get approval for this drug, it’ll be the first time any aging drug, any lifespan drug, has been approved for any species,” he said. “I hope it’ll open some doors scientifically. It’ll show that here’s a way that we can actually prove that this works.”