Matt Kaeberlein

Matt Kaeberlein built his academic career at the University of Washington in Seattle studying evolutionarily conserved mechanisms of aging, including the target of rapamycin (TOR) pathway across yeast, worms, flies, and mammals [1]. With Daniel Promislow, he co-founded the Dog Aging Project in 2014 with a $200,000 seed grant from the University of Washington, later expanded with National Institute on Aging funding starting in 2018 [2]. The project has enrolled close to 40,000 companion dogs in a long-term observational study, with a smaller arm testing whether rapamycin extends healthy lifespan in pet dogs, an approach that uses a genetically diverse, environmentally varied population that ages roughly seven times faster than humans and shares their households [2].

In 2023 Kaeberlein co-authored, with his daughter Tammi Kaeberlein and collaborators including physicians from AgelessRx, a survey study in the journal GeroScience covering 333 adults with a history of off-label rapamycin use compared with 172 adults who had never used it [3]. The paper, titled "Evaluation of off-label rapamycin use to promote healthspan in 333 adults," reported that rapamycin could be used safely in adults of normal health status based on self-reported side-effect data, while explicitly noting the study design (a retrospective survey, not a randomized trial) limits what it can establish about efficacy [3]. Several co-authors, including physicians affiliated with AgelessRx, have direct commercial interests in rapamycin prescribing services, a relationship disclosed in the paper's author affiliations [3].

Kaeberlein has since left his University of Washington faculty position to found and run Optispan Geroscience, a company offering geroscience consulting and, through its affiliated Optispan Clinic, biomarker testing and longevity-focused medical guidance directly to paying clients [3]. This is a direct commercial extension of his academic rapamycin and biomarker research into a fee-for-service business model.

On the Dog Aging Project itself, Kaeberlein has been candid in public interviews that funding continuity has been a recurring challenge; community discussion among longevity enthusiasts following his podcast appearances describes a period in which federal funding for the rapamycin trial arm was reduced, prompting private donations, including from other longevity-focused physicians, to keep parts of the study running [4]. This funding structure means the trial's ultimate completion has depended partly on the same community of rapamycin advocates whose commercial and personal interests could benefit from a positive result, a dependency worth noting even though it does not by itself invalidate the trial's design or data collection methods.

Kaeberlein's public statements on rapamycin dosing have generally emphasized that effects are dose-dependent and that pulsed, once-weekly or biweekly regimens used by longevity self-experimenters differ substantially from the daily immunosuppressive doses used in organ transplant patients, a distinction that matters for interpreting side-effect data from either population [3]. He has been more willing than some academic peers to state publicly that current human safety data, while reassuring at the doses studied, remain based on self-report rather than controlled trial follow-up.

The plain takeaway: Kaeberlein has produced some of the only published human safety data on off-label rapamycin use, based on hundreds of real users, but the underlying data are self-reported survey responses, several co-authors and the funding base carry a commercial interest in a favorable readout, and no completed randomized controlled trial in humans has yet confirmed either the safety or efficacy claims commonly cited from this work.