Loyal: Betting That Ageing Itself Is Treatable

Veterinary medicine has spent decades treating the diseases that come with old age in dogs. Arthritis gets a prescription. Kidney decline gets a diet change. Heart disease gets a specialist referral. Loyal, a San Francisco-based clinical-stage veterinary medicine company, is asking a different question: what if a drug could directly slow the ageing process behind those diseases?

Loyal develops drugs that target the biological processes behind canine ageing. The company describes them as the first drugs intended to extend both the lifespan and the healthspan of dogs. An FDA approval would make one of them the first lifespan-extension drug approved for any species, human or animal.

A Founder Who Started With Humans and Landed on Dogs

Celine Halioua founded Loyal in late 2019 after studying neuroscience at the University of Texas at Austin and health economics at Oxford University. She had worked as chief of staff at The Longevity Fund, an investment vehicle Laura Deming built around human lifespan science. Halioua concluded that dogs offered a faster path to proving out longevity science, since their compressed lifespans let researchers see results in years rather than decades. Enough of the biology overlaps that findings in dogs could eventually inform human treatments.

Halioua has said that early pitches for a longevity drug in 2019 drew laughter, not term sheets. Six years on, that scepticism has given way to regulatory milestones and hundreds of millions in funding.

What Loyal Has Built So Far?

Loyal currently has three drug candidates in development, each targeting a distinct driver of canine ageing. LOY-002, the company’s lead program, is a daily prescription pill aimed at senior dogs at least 10 years old and weighing 14 pounds or more. It targets metabolic dysfunction, which the company considers a core driver of age-related disease. Halioua has described the mechanism as an attempt to mimic the effects of caloric restriction without cutting a dog’s food intake.

In order to counteract the shortened lifespans of large and giant breed dogs, LOY-001 and LOY-003 are designed to target the rapid ageing driven by a specific hormone. Instead of a daily pill, veterinarians would administer these therapies as long-acting injections just a few times a year. Both drugs work by addressing the overexpression of insulin-like growth factor 1, which the company believes causes bigger dogs to age faster.

Loyal’s clinical progress centres on the STAY study, the pivotal trial for LOY-002 that dosed its first dog in December 2023. The company expects the trial to run for roughly four years. It follows a double-blind, placebo-controlled design and enrolled 1,300 senior dogs across 70 veterinary clinics nationwide. Loyal calls it the largest clinical trial in veterinary medicine. The company also says the FDA has formally concurred with its design, a distinction no other longevity study has received.

The trial has already produced regulatory progress ahead of its scheduled completion. In February 2025, the FDA’s Centre for Veterinary Medicine accepted the Reasonable Expectation of Effectiveness section of LOY-002’s application under the agency’s Expanded Conditional Approval pathway for conditional market access. A second milestone followed in December 2025, when the agency accepted the drug’s Target Animal Safety package, based on a dosing study and field data from more than 400 STAY trial dogs. Dr Ellen Ratcliff, Loyal’s VP of Clinical and Veterinary Medicine, described the safety clearance as an important vote of confidence in the company’s mission.

Revenue Still Pending, Funding Already Flowing

Despite that regulatory progress, Loyal has not generated commercial revenue. As a clinical-stage company, it does not expect meaningful sales until LOY-002 clears its remaining FDA requirements and reaches veterinarians. At that point, the company plans to sell it as a veterinarian-prescribed daily tablet. Until then, capital from investors funds the trials and the regulatory work behind them.

Loyal has raised more than $250 million since its founding, according to the company. Early backers included Khosla Ventures, Bain Capital, and Valour Equity Partners. In February 2026, age1, the successor to Laura Deming’s original Longevity Fund, led a $100 million Series C investment in Loyal, with Baillie Gifford also participating. Tom Slater of Baillie Gifford said in a company press release that Loyal has built the foundations for a substantial business in a large market.

What Comes Next

With that funding in hand, Loyal’s near-term plan is to finish the STAY trial and file its final Expanded Conditional Approval requirement. Halioua has said the company hopes to complete that filing this year, which would start a roughly six-month FDA review. A favourable outcome would make LOY-002 the first FDA-approved lifespan extension drug for any species. It would also clear the way for LOY-001 and LOY-003, which are pursuing separate paths for large and giant breed dogs. The next 12 months, more than any funding round to date, will decide how much of that roadmap becomes a product veterinarians can actually prescribe.