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A biotechnology company developing drugs to extend healthy lifespan in dogs, working through the veterinary regulator that will consider lifespan itself as an indication.
Loyal is a San Francisco biotechnology company, incorporated in Delaware in 2019 as Cellular Longevity, Inc.,1 that develops drugs intended to extend the healthy lifespan of dogs. Its founder, Celine Halioua, began her career at the Longevity Fund, the venture firm started by Laura Deming.2 Its interest for geroscience is procedural as much as pharmacological: the veterinary arm of the US Food and Drug Administration will entertain "extension of lifespan" as a drug indication, and its human counterpart will not. As of November 2026 the agency had accepted the effectiveness sections for all three of Loyal's drug candidates and the safety section for one, but had approved none of them,34 and no study had shown that a Loyal drug lengthens a dog's life.56
The company's premise is that dogs are closer to people than laboratory mice are, and closer to a marketed product than any human aging drug. Companion dogs share human households, diets and sedentary habits. They develop cancer, osteoarthritis and a cognitive decline syndrome resembling dementia, and they are genetically diverse in a way inbred mouse colonies are not. They also die within about a decade, which makes a survival endpoint affordable. A trial powered on how long the animals live reads out in years, where a human equivalent would need decades; that arithmetic is what pushed the proposed TAME trial in people onto a composite endpoint of age-related disease instead.
Loyal is small next to the best-capitalized longevity companies such as Altos Labs. By its own count it has raised more than $250 million since its founding,7 and it runs three programmes designated LOY-001, LOY-002 and LOY-003.
Loyal attracted little public attention until late 2023, when the first FDA finding drew wide press coverage, some of which described the milestone as an approval. It was not one. The company's projected dates have since moved. In February 2024 it said veterinarians might be able to prescribe LOY-002 as soon as early 2025,8 and a year later it hoped to complete all the regulatory requirements by the end of 2025.9 In January 2026, according to the trade publication dvm360, it expected the last major section, manufacturing, to be reviewed in 2027.10 As of November 2026 its website lists that section as in progress, and no Loyal product is on sale, conditionally or otherwise.4
LOY-001 and LOY-003 target the same axis in large and giant breeds. LOY-001 is a long-acting injection that a veterinarian would give every three to six months.11 LOY-003 is a daily tablet: the compound CRN01941, which Crinetics Pharmaceuticals developed for acromegaly in people and licensed to Loyal for veterinary use in 2023.12 The company intends LOY-001 for dogs aged seven or older weighing at least 40 lb and LOY-003 for dogs aged five or older weighing at least 60 lb,13 and says both lower growth hormone and IGF-1.3
The rationale is the company's own reading of canine genetics. Within the domestic dog, larger body size correlates strongly with a shorter life, and large breeds appear to age faster rather than to start from a worse baseline.14 A single variant near the IGF1 gene is a major determinant of small size across breeds,15 and circulating insulin-like growth factor 1 rises with body weight across breeds.16 Loyal's proposition is that lowering IGF-1 in a large dog toward the level typical of a small one should slow that acceleration.
The underlying pathway has a strong pedigree. Reduced insulin and IGF-1 signalling extends lifespan in nematodes, flies and mice, from the daf-2 mutants characterized by Cynthia Kenyon to growth-hormone-deficient dwarf mice, and nutrient sensing recurs throughout the Hallmarks of aging. Applying that literature to large dogs is an inference, though. The size-lifespan correlation is well documented, but the claim that IGF-1 causes it is a hypothesis, and no published trial has shown that lowering IGF-1 lengthens a dog's life.
The evidence behind the 2023 finding is described only by the company. Loyal says the effectiveness section, more than 2,300 pages, combined interventional studies of LOY-001 in laboratory dogs used as a model of accelerated aging with an observational, drug-free study of 451 companion dogs, which it used to link the drug's biological effects to quality of life and health outcomes.11 The New York Times reported at the time that the research was unpublished, and that it suggested the drug reduces IGF-1 and might curb age-related rises in insulin.5 Loyal says full approval of either large-dog drug would require large, long-term efficacy trials similar to STAY, which it describes as planned.17
LOY-002 is a daily tablet for dogs aged 10 or older and weighing at least 14 lb. The company calls it a caloric restriction mimetic, meant to deliver the metabolic benefits of dietary restriction without weight loss or appetite suppression.9 It says the drug acts by improving insulin sensitivity and lowering insulin,4 but has not named the compound and describes the exact mechanism as confidential.17 It frames the goal as extending healthy life rather than postponing death, the canine version of Compression of morbidity. The first clinical use was a 2023 pilot in 60 companion dogs aged 7 to 10, run mainly to see how the drug affected biomarkers that change with age.18
STAY is LOY-002's pivotal effectiveness study. In March 2023 the Center for Veterinary Medicine concurred with its protocol, which the company describes as agreement that a positive result would support approval.1918 The first dog was dosed in February 2024.8 Enrolment closed in July 2025 at 1,300 dogs, screened from more than 1,500, across 72 clinics, nearly three quarters of which had never run a clinical trial.20 The study is double-blind and placebo-controlled, with each dog given an even chance of receiving the drug. Owners commit to up to four years, and the trial compares lifespan, health and quality of life between the two groups.6 Loyal calls STAY the largest clinical trial in the history of veterinary medicine,7 and Halioua has said it is well powered to detect lifespan and healthspan extension.2
Treatment assignments stay blinded until the study ends,6 so no efficacy result had been released as of November 2026. The company's stated aims are modest by the standards of longevity rhetoric. In 2023, discussing its large-dog drug, Halioua said Loyal would aim to claim "at least one year" of healthy lifespan extension, and that "these are definitely not immortality or radical life-span-extension drugs."5
The safety section accepted in January 2026 rested, according to the company, on a safety study at one, three and five times the intended dose with no clinically significant adverse events, plus data from more than 400 dogs given LOY-002 for up to a year, which the company describes in one place as field data and in another as laboratory studies.2117
Human healthspan research has nothing comparable: a placebo-controlled trial in a naturally aging, free-living mammal population, powered on how long the animals live rather than on a movement in an Epigenetic clocks reading or another unvalidated surrogate.
In the United States a drug for dogs is approved through a new animal drug application reviewed by the Center for Veterinary Medicine. The application is assembled in technical sections, covering effectiveness, target animal safety, manufacturing chemistry and labelling, and each is reviewed as it is submitted. Full approval requires substantial evidence of effectiveness, the same statutory phrase used for human drugs.
Conditional approval sits alongside it. The pathway was created for minor species and minor uses, and in 2018 it was extended to drugs for major species that address serious conditions or unmet needs where a conventional effectiveness study would be particularly difficult.22 Loyal calls this route expanded conditional approval. It lets a sponsor market a drug by prescription for up to five years while assembling the evidence that full approval demands, and a drug that has not shown full effectiveness by the end of that period comes off the market. The FDA publishes a Freedom of Information summary of the data on approval.23 The entry bar is lower: a reasonable expectation of effectiveness rather than substantial evidence. Loyal argues that a canine lifespan study is exactly what the provision was written for. The route is little used. A March 2026 Government Accountability Office review counted 11 conditional approvals of new animal drugs in fiscal years 2018 through 2025, all for major species, and found that the pathway and other incentives had had a limited effect on drug development. It added that two more drugs had been conditionally approved by 31 January 2026.24
What the FDA agreed to, preciselyThe Center for Veterinary Medicine has accepted the reasonable expectation of effectiveness section for LOY-001 in November 2023, for LOY-002 in February 2025 and for LOY-003 in September 2026, and the target animal safety section for LOY-002 in January 2026.119321 Each is a finding on one technical section of a conditional-approval application. None is a conditional approval, a full approval, or a finding that a drug extends any animal's life. As of November 2026 LOY-002's manufacturing section was still in progress and no Loyal drug was approved.4
Human medicine has no equivalent. No regulator recognizes aging as an indication in people, no surrogate marker of aging has been qualified for registrational use, and a human survival trial would run for decades. For those reasons Calico Life Sciences and its peers develop drugs for named diseases and argue that the biology generalizes, Nir Barzilai and colleagues have spent years arguing a composite of age-related events into acceptability as an endpoint, and the XPRIZE Healthspan competition had to invent its own. Veterinary medicine reached a lifespan indication first because the arithmetic is easier, not because the science is further along.
The academic version of the same bet is the Dog Aging Project, a separate effort based at the University of Washington and founded by Daniel Promislow and Matt Kaeberlein with colleagues at other institutions. It runs an open-science cohort of tens of thousands of companion dogs whose owners contribute health data,25 and within it TRIAD, a randomized placebo-controlled trial of Rapamycin in companion dogs.26 An earlier ten-week pilot from the same investigators reported improved cardiac measures in two dozen middle-aged dogs.27 The project is academic and tests a generic drug, whereas Loyal is a company developing proprietary compounds toward a marketed product. Coverage frequently confuses the two.
Neither is the first intervention to move canine lifespan. A long-running paired-littermate study in Labrador retrievers found that dogs fed a restricted diet lived roughly two years longer than their freely fed siblings.28 That remains the best-supported way to extend a dog's life, and it is the same dietary restriction result that anchors the rodent literature. Loyal cites it as the precedent for LOY-002.9
A dog result is not a human resultEvery claim in this area concerns dogs, and as of November 2026 no drug had been shown in a controlled trial to extend dogs' lives.56 If STAY reported a survival benefit, it would establish that a drug extended lifespan in one population of senior companion dogs, not that it restored youth; a human programme would still have to begin again at first-in-human safety, against an indication no regulator accepts. The natural human experiment on the IGF-1 axis is instructive: people with growth hormone receptor deficiency have strikingly little cancer and diabetes, without a demonstrated increase in lifespan.29
Loyal is venture-funded and publishes no financial statements. By its own account it raised a $45 million Series B led by Bain Capital Ventures in March 2024, taking its total above $125 million;30 a further $22 million in February 2025, taking it above $150 million;9 and a $100 million Series C led by age1, with Baillie Gifford participating, in February 2026, taking it above $250 million. The company said the Series C would fund the remaining regulatory work on LOY-002 and preparation for launch.7
Its commercial model is a prescription drug sold through veterinarians and paid for out of pocket, since pet insurance rarely covers preventive medication. In 2023 Halioua estimated that LOY-001 would cost "mid-double-digit dollars per month".5 A daily tablet for the rest of a senior dog's life is a recurring cost, so uptake would sort by household income along the lines the human access debate anticipates, with the added complication that the patient cannot consent.
Specialists have generally welcomed the regulatory precedent while being careful about what it shows. A survival-powered trial in a free-living mammal is better evidence than most of what the field produces, including the mouse work behind Senolytics. Veterinary approval is also a real bar, unlike a supplement pathway, because the agency reviews safety, manufacturing and effectiveness.
Criticism runs in several directions. The press has repeatedly reported the effectiveness findings as approvals, a confusion the unfamiliar terminology invites and one that flatters the company however it arises. The IGF-1 rationale rests on a correlation whose causal reading is unsettled. And conditional approval by design permits sale before effectiveness is established, so owners could pay for years for a drug whose benefit remains unproven. That trade-off is deliberate, but it lands differently in a mass market of anxious owners than in a veterinary specialty setting.
Veterinarians and ethicists have added their own objections. Kate Creevy, chief veterinary officer of the Dog Aging Project, said in 2023 that she would value a longer life only if the added time were healthy: "I don't want to make my dog live an extra two years in poor health."5 In 2025 the veterinary oncologist Daniela Korec told Slate she approached LOY-002 with "a dose of skepticism" until she could see its full composition and retrospective data, and the bioethicist Jessica Pierce argued that such drugs serve what owners want rather than dogs' welfare.31
Is the veterinary route a shortcut to human geroscience?Proponents argue that a positive canine survival result would be the first controlled demonstration that a drug slows aging in a large outbred mammal sharing the human environment, and would pressure regulators to define a human aging endpoint. Skeptics reply that dogs metabolize drugs differently, and that the human bottleneck was never a lack of evidence from another species: the problem is that "aging" has no legal status as a condition to treat.
The events worth watching are narrow. They are whether LOY-002's manufacturing section is accepted and a conditional approval follows, whether STAY reports a survival difference and how large it is, and whether a conditional approval converts to a full one inside the five-year window rather than lapsing. A drug marketed for years and then withdrawn for want of evidence would do more damage to the argument that lifespan can be an indication than never having tried.
The most useful outcome may be a negative one. A well-run placebo-controlled trial reporting no survival effect would be the first clean null for a candidate geroprotector in a naturally aging mammal outside the laboratory, and the field has produced far more positive mouse results than it has learned to interpret. So far the FDA has conceded only that the question can be asked; no one has yet answered it.
statementCellular Longevity, Inc. Form D notice of exempt offering, US Securities and Exchange Commission, filed 16 January 2020 (CIK 0001799919). https://www.sec.gov/Archives/edgar/data/1799919/000179991920000001/primary_doc.xml↩Lists Delaware as the jurisdiction and 2019 as the year of incorporation, with Halioua as executive officer and director.
statementHalioua, C. "Loyal's Series C: $100M to advance the first longevity drug." Loyal company blog, 11 February 2026. https://loyal.com/posts/100m-for-first-longevity-drug ↩ ↩2
statementLoyal. "Loyal Earns Third Efficacy Acceptance (RXE) from the FDA for Canine Lifespan Extension." Press release via Business Wire, 16 September 2026; reprinted by FinancialContent. https://www.financialcontent.com/article/bizwire-2026-9-16-loyal-earns-third-efficacy-acceptance-rxe-from-the-fda-for-canine-lifespan-extension ↩ ↩2 ↩3
statementLoyal. Company home page, loyal.com, accessed 1 November 2026. https://loyal.com/↩ ↩2 ↩3 ↩4Lists LOY-002's effectiveness and safety sections as accepted and its manufacturing section as in progress, with the note that FDA approval is not guaranteed.
newsAnthes, E. "Could a Drug Give Your Pet More Dog Years?" The New York Times, 28 November 2023; reprinted by Boston.com, 29 November 2023. ↩ ↩2 ↩3 ↩4 ↩5 ↩6
statementLoyal. "Clinical trials" (STAY study page), loyal.com, accessed 1 November 2026. https://loyal.com/clinical-trials ↩ ↩2 ↩3 ↩4
statementLoyal. "Loyal raises $100M Series C, led by age1, to advance the first canine longevity drug." Press release, 11 February 2026. https://loyal.com/posts/series-c-announcement ↩ ↩2 ↩3
statementHalioua, C. "Meet Boo, the first dog dosed in our LOY-002 pivotal study for extending healthy lifespan in dogs of nearly all sizes." Loyal company blog, 1 February 2024. https://loyal.com/posts/meet-boo-first-stay-study-dog-dosed ↩ ↩2
statementHalioua, C. "Not just for big dogs! Our senior dog program receives preliminary FDA efficacy acceptance (RXE)." Loyal company blog, 26 February 2025. https://loyal.com/posts/loy-002-receives-rxe-from-the-fda ↩ ↩2 ↩3 ↩4 ↩5
newsCoppock Crossley, K. "Lifespan extension drug in development for senior dogs reaches a new milestone." dvm360, 13 January 2026. https://www.dvm360.com/view/lifespan-extension-drug-in-development-for-senior-dogs-reaches-a-new-milestone ↩
statementHalioua, C. "FDA Center for Veterinary Medicine agrees Loyal's data supports reasonable expectation of effectiveness for large dog lifespan extension." Loyal company blog, 28 November 2023. https://loyal.com/posts/loyal-announces-historic-fda-milestone-for-large-dog-lifespan-extension-drug↩ ↩2 ↩3A company reporting regulatory correspondence about itself; the agency does not publish findings at this stage of a review, so no independent document confirms it.
statementHalioua, C. "Announcing our partnership with Crinetics Pharmaceuticals." Loyal company blog, 11 August 2023. https://loyal.com/posts/announcing-our-partnership-with-crinetics-pharmaceuticals ↩
statementLoyal. "Products in development," loyal.com, accessed 1 November 2026. https://loyal.com/products ↩
paperKraus, C., Pavard, S. and Promislow, D.E.L. "The Size–Life Span Trade-Off Decomposed: Why Large Dogs Die Young." The American Naturalist, 2013.↩Decomposes the correlation and attributes it mainly to faster aging in large breeds rather than higher baseline mortality.
paperSutter, N.B. et al. "A Single IGF1 Allele Is a Major Determinant of Small Size in Dogs." Science, 2007. ↩
paperGreer, K.A., Hughes, L.M. and Masternak, M.M. "Connecting serum IGF-1, body size, and age in the domestic dog." Age 33(3):475-483, 2011. https://doi.org/10.1007/s11357-010-9182-4↩Cross-sectional serum measurements across breeds; the relationship with weight varied with spay and neuter status.
statementLoyal. "Product brief for veterinarians," version 7, undated, accessed 1 November 2026. https://loyal.com/downloads/Loyal-product-brief-for-vets-v7.pdf ↩ ↩2 ↩3
statementLoyal. "Our LOY-002 clinical pilot study is now fully enrolled." Company blog, 11 April 2023. https://loyal.com/posts/our-loy-002-clinical-pilot-study-is-now-fully-enrolled ↩ ↩2
statementLoyal. "Loyal's latest milestone: the first longevity clinical study design supported by the FDA." Company blog, 10 March 2023. https://loyal.com/posts/loyals-latest-milestone-the-first-longevity-clinical-study-design-supported-by-the-fda ↩
statementRatcliff, E. "The STAY study finishes enrollment: A big day for dog-kind!" Loyal company blog, 14 July 2025. https://loyal.com/posts/stay-finishes-enrollment ↩
statementMcKenzie, B. "One step closer to a dog longevity drug: What LOY-002's safety milestone means to a practicing vet." Loyal company blog, 13 January 2026. https://loyal.com/posts/loy-002-tas ↩ ↩2
lawAnimal Drug and Animal Generic Drug User Fee Amendments of 2018, United States.↩The amendments extended conditional approval beyond minor uses and minor species to certain drugs for major species addressing serious conditions or unmet needs.
statementHalioua, C. "What is FDA conditional approval?" Loyal company blog, 16 April 2024. https://loyal.com/posts/what-is-fda-conditional-approval ↩
reportUS Government Accountability Office. Animal Drugs: Strengthening Federal Incentives Could Help Address Unmet Animal Health Needs. GAO-26-107896, 3 March 2026. https://www.gao.gov/products/gao-26-107896↩Reviews the animal-drug incentive programmes generally; it does not discuss Loyal or lifespan indications.
paperCreevy, K.E. et al. "An open science study of ageing in companion dogs." Nature, 2022. ↩
paperKaeberlein, M., Creevy, K.E. and Promislow, D.E.L. "The dog aging project: translational geroscience in companion animals." Mammalian Genome, 2016. ↩
paperUrfer, S.R. et al. "A randomized controlled trial to establish effects of short-term rapamycin treatment in 24 middle-aged companion dogs." GeroScience, 2017.↩Ten weeks of dosing in two dozen dogs; the reported cardiac changes were secondary measures in a trial not powered for clinical outcomes.
paperKealy, R.D. et al. "Effects of diet restriction on life span and age-related changes in dogs." Journal of the American Veterinary Medical Association, 2002.↩Forty-eight Labrador retrievers in littermate pairs, one of each pair fed about a quarter less; a small study, but paired and lifelong.
paperGuevara-Aguirre, J. et al. "Growth hormone receptor deficiency is associated with a major reduction in pro-aging signaling, cancer, and diabetes in humans." Science Translational Medicine, 2011.↩The Ecuadorian cohort showed almost no cancer or diabetes, but no increase in average lifespan; other causes of death rose.
statementHalioua, C. "$125M to extend dog lifespan." Loyal company blog, 21 March 2024. https://loyal.com/posts/125m-to-extend-dog-lifespan ↩
newsHanson, K. "This Pill Promises to Give Your Dog More Years. You Might Not Like What Comes With Them." Slate, 23 April 2025. https://slate.com/technology/2025/04/dogs-pets-pill-longevity-extend-lifespan-loyal-veterinary-ethics.html ↩