The life of a pet dog follows a predictable trajectory. Over time, the floppy-eared puppy that keeps falling asleep in his food bowl will become a lanky-legged adolescent with an insatiable interest in squirrels — before eventually settling into adulthood as a canine creature of habit, with a carefully chosen napping location and a well-rehearsed greeting ritual.
But as the years progress, his joints will stiffen and his muzzle will gray. And one day, which will inevitably arrive too soon, his wagging tail will finally still.
“When you adopt a dog, you’re adopting future heartbreak,” said Emilie Adams, a New Yorker who owns three Rhodesian Ridgebacks. “It’s worth it over time because you just have so much love between now and when they go. But their life spans are shorter than ours.”
In recent years, scientists have been chasing after drugs that might stave off this heartbreak by extending the lives of our canine companions. On Tuesday, the biotech company Loyal announced that it had moved one step closer to bringing one such drug to market. “The data you provided are sufficient to show that there is a reasonable expectation of effectiveness,” an official at the U.S. Food and Drug Administration informed the company in a recent letter. (Loyal provided a copy of the letter to The Times.)
That means that the drug, which Loyal declined to identify for proprietary reasons, has met one of the requirements for “expanded conditional approval,” a fast-tracked authorization for animal drugs that fulfill unmet health needs and require difficult clinical trials. The drug is not available to pet owners yet, and the F.D.A. must still review the company’s safety and manufacturing data. But conditional approval, which Loyal hopes to receive in 2026, would allow the company to begin marketing the drug for canine life extension, even before a large clinical trial is complete.
“We’re going to be going for claiming at least one year of healthy life span extension,” said Celine Halioua, the founder and chief executive of Loyal.
Whether the drug will actually deliver on that promise is unknown. Although a small study suggests LOY-001 might blunt metabolic changes associated with aging, Loyal has not yet demonstrated that it lengthens dogs’ lives.
But the letter, which came after years of discussion between Loyal and the F.D.A., suggests that the agency is open to canine longevity drugs, Ms. Halioua said.
Celine Halioua, the founder and chief executive of Loyal, with her aging Rottweiler, Della.Credit…Loyal
More are in the pipeline. A team of academic researchers is currently conducting a canine clinical trial of rapamycin, which has been shown to extend the lives of lab mice. And Loyal is recruiting dogs for a clinical trial of another drug candidate, dubbed LOY-002.
These developments are a sign of the accelerating pace of the science and the seriousness with which researchers and regulators are taking a field that once seemed like science fiction. They also raise questions about what it might mean to succeed, said Daniel Promislow, a biogerontologist at the University of Washington and a co-director of the Dog Aging Project, which is conducting the rapamycin trial.
“What if it works?” he said. “What are the implications?”
Lapping at the fountain of youth
Aging may be an inevitability, but it is not an unyielding one. Scientists have created longer-lived worms, flies and mice by tweaking key aging-related genes.
These findings have raised the tantalizing possibility that scientists might be able to find drugs that had the same life-extending effects in people. That remains an active area of research, but canine longevity has recently started to attract more attention, in part because dogs are good models for human aging and in part because many pet owners would love more time with their furry family members.
“There’s not a lot you wouldn’t do if you could stack the deck in your favor to preserve the life of your hairy, four-legged child,” said Ms. Adams, the Rhodesian Ridgeback owner.
The drugs currently under investigation act in different ways.Rapamycin, which has also attracted intense interest as a potential longevity drug for humans, inhibits a protein known as mTOR, which regulates cell growth and metabolism.
Earlier this year, a team of scientists including Dr. Promislow and some of his colleagues at the Dog Aging Project published an analysis of dogs that had been randomly assigned to receive either a low dose of rapamycin or a placebo for six months. Although the sample size was small, 27 percent of dog owners whose pets received the drug reported improvements in health or behavior, including increases in activity or playfulness, compared with 8 percent of owners whose dogs received a placebo.
LOY-001, an extended-release implant intended for large, adult dogs, is designed to modulate a different growth-related compound: insulin growth factor-1, or IGF-1. The IGF-1 pathway has been associated with aging and longevity in several species; in dogs, it is known to play a key role in determining body size. Although the idea remains unproven, some scientists hypothesize that high IGF-1 levels drive both rapid growth and accelerated aging in large dogs, which generally have shorter life spans than small ones.
Loyal’s own research, which has not yet been published, suggests that LOY-001 does reduce IGF-1 levels in dogs and that it might curb aging-related increases in insulin; an observational study of nearly 500 dogs also suggested that lower insulin levels were correlated with reduced frailty and a higher quality of life.
“It’s quite an exciting approach,” said Colin Selman, a biogerontologist of aging at the University of Glasgow, who was not involved in the research and had not personally reviewed the company’s data.
But proving that a drug can actually extend canine lives will require large, time-consuming clinical trials. Although some are currently underway, it will be at least several more years before the results are in. And regardless of the drug, researchers will need to demonstrate that it adds good, healthy years to a dog’s life, rather than just drawing out their decline, experts said.
“If it proves true that it extends life span, I’m only interested in that if the period of life that is extended is good quality life,” said Dr. Kate Creevy, a veterinarian at Texas A&M and the chief veterinary officer of the Dog Aging Project.“I don’t want to make my dog live an extra two years in poor health.”
It is too soon to say what longevity drugs will cost, but Ms. Halioua predicted that LOY-001 would work out to “mid-double-digit dollars per month.”
For some owners, cost will not be a deterrent, said Karen Cornelius of Illinois, who has owned mastiffs and other “giant” breeds for decades. Many died when they were about 9 years old, said Ms. Cornelius, who runs several Facebook groups for owners of giant dogs.
“We were just having a discussion on one of my forums yesterday about how short-lived they were, and how people would give almost anything if they could extend that life,” she said.
Some ethicists worried that this enthusiasm could be exploited, especially if the drugs are advertised as fountains of canine youth while questions of long-term safety and efficacy remain unresolved. The dogs themselves cannot give consent, they noted.
“Is it in their best interest to live a little bit longer when there’s some risk to taking these drugs?” said Rebecca Walker, a philosopher and bioethicist at the University of North Carolina at Chapel Hill, who said she would not give a longevity drug to her golden retriever. “Or is it really in the best interest of their owners, who are very attached to them?”
So far, the worst side effect of LOY-001 has been mild and temporary gastrointestinal distress, Ms. Halioua said, although she acknowledged that the bar for safety would be “extremely, extremely, extremely high.”
Longevity drugs are intended for healthy dogs, which changes the risk-benefit calculus. “It’s one thing if a dog is on death’s door and you’re giving them some late-breaking treatment,” said Bev Klingensmith, a Great Dane breeder in Iowa who also has a Great Dane and a golden retriever of her own. “Giving my young, healthy dog a brand-new drug would seem a little scary.”
Even drugs that deliver on all their promises will raise ethical questions. “If animals are living longer, do we have the resources and commitment to provide lives worth living?” Dr. Anne Quain, a veterinarian and an expert on veterinary ethics at the University of Sydney, said in an email. “What if we see more dogs outliving their owners?”
Reforming the breeding practices that have contributed to life-shortening health problems in many dogs and expanding access to basic veterinary care might be a better way to improve canine lives, she added. “We can save many ‘dog years’ by ensuring that as many dogs have access to that care as possible,” she said.
And while scientists gather more data on potential longevity drugs, there are steps that dog owners can now take to foster healthier aging, experts said, including keeping their dogs lean and providing ample exercise and mental stimulation.
Ms. Halioua admitted to having a soft spot for senior dogs. “They just want a nice bed to sleep on,” she said, as her elderly Rottweiler, Della, napped. Della, who has lymphoma and dementia, is not on LOY-001 because enrolling her in the company’s studies would present a conflict of interest, Ms. Halioua said, but the dog seemed happy, she noted.
Ultimately, even if scientists can delay a pet owner’s heartbreak, they are unlikely to prevent it altogether. “These are definitely not immortality or radical life-span-extension drugs,” Ms. Halioua said in an email. She added, “Nothing we are developing could make a dog live forever.”