She doesn’t make the jump to the window ledge in one go anymore.
The 2am sprint down the hallway stopped happening months ago.
She still purrs when you come home. She just takes a little longer to get there.
None of that is “just old age”. It is biology — and for the first time, biology we can act on.
For most of veterinary history there wasn’t. You brought your cat in, the bloodwork came back “normal for her age”, and you went home with nothing to do but watch.
You are the kind of owner who reads the lab values. Who notices the change in the jump before anyone else does. Who has already done the arithmetic on how many years are likely left.
That instinct was right. What has changed is that the biology of feline aging is now a target — not a metaphor.
drug approved for feline hypertrophic cardiomyopathy — and the molecule is sirolimus, the one we dispense.
In March 2025 the FDA granted conditional approval to a delayed-release sirolimus tablet for managing ventricular hypertrophy in cats with subclinical HCM, a disease affecting as many as one in seven cats and one that had never had an approved drug. Conditional means the FDA found a reasonable expectation of effectiveness while the remaining data is collected — further than any other option for this disease has ever reached.
Lifespan is a number on a chart. Healthspan is whether she still does the things that make her recognisably herself.
Rapamycin acts on mTOR — the pathway that decides whether cells grow or repair themselves. Each card leads with what has been established, and says plainly where the line is.
Sirolimus is the first and only drug ever approved for feline HCM — conditionally approved by the FDA in March 2025 for managing ventricular hypertrophy in cats with subclinical disease. In the placebo-controlled feline trial, cats given rapamycin had no more side effects than cats given placebo. The approval covers managing the hypertrophy, not curing the disease.
Chronic kidney disease is the leading cause of death in cats over five, and it is driven by fibrosis and cellular senescence — both mTOR-linked. The REVERSE trial is testing rapamycin in cats with CKD right now at Ohio State, led by feline renal specialist Dr Jessica Quimby, and is still recruiting. It has not reported results.
mTOR is switched on in 56.9% of feline mammary carcinomas and persistently active in feline cutaneous squamous cell carcinoma — which is precisely why the pathway is being investigated as a target in these tumours. mTOR inhibition is already established in human oncology. No trial has yet shown that rapamycin treats or prevents either cancer in cats.
Across mammalian studies rapamycin extends healthy lifespan by up to 14%, and it does so even when started in late middle age — the most reproducible result in the field. It works by restoring autophagy, the cellular cleanup process whose biology won the 2016 Nobel Prize. In cats specifically, the lifespan question is being studied, not settled.
Her owner brought her in for a dental. The vet heard a gallop rhythm, and the echocardiogram found what the stethoscope suspected: hypertrophic cardiomyopathy, still subclinical. No signs. No symptoms. A heart wall already thicker than it should be.
The conversation that follows that diagnosis used to be short. Monitor. Recheck in six months. Hope it stays slow.
Instead her cardiologist built a protocol: weight-calibrated, once-weekly, with echocardiography tracking the thing that actually matters. Eighteen months on, Sisu is thirteen, and the wall measurement has held.
One cat’s course is not a result you should expect. Individual outcomes vary, and this story is not a medical claim.
Most cats that start are healthy. The point is to act before there is a crisis to react to.
It is not right for every cat. Diabetes or impaired glucose regulation, active infection, significant liver disease, planned surgery, or pregnancy all rule it out — so check each of these with your own veterinarian before starting.
The molecule is the easy part. What makes it work — and what makes it safe — is everything around it.
0.4 mg, 1.2 mg or 2.4 mg, scaled to body weight. Longevity dosing is a fraction of the dose used in transplant medicine, and it is intermittent rather than daily. Confirm the exact strength with your own vet before starting.
A delayed-release, acid-resistant tablet. Flavoured oral suspensions exist for cats that refuse tablets — the protocol only works if it is actually given.
Health history, current medications and baseline bloodwork, all with your own vet. Rapamycin is metabolised through CYP3A4, so interactions are checked rather than assumed.
Periodic bloodwork, weight, and where HCM is involved, echocardiography — measuring the wall itself, not just how she seems. Plan these rechecks with your own vet.
Given properly, this is a monitored medical protocol. Given without oversight — wrong dose, no screening, no bloodwork, unchecked interactions — it is neither safe nor useful. That is why your own vet belongs in it from the first dose.
Rapamycin is a prescription medicine. Use it only under the guidance of your own veterinarian.
Already have a vet who knows your cat? Bring them the protocol. We will share the published research behind the dose and the monitoring, so your vet can make the call.
Read the science →The strength for your cat’s body weight, one box at a time — order again when you need more. Check the strength with your own vet first.
See the cat medicines →What is another two good years with her worth? We can’t price that. We can tell you what the programme costs, and exactly what is in it.
Longevity medicine is not about getting hold of a molecule. It is about the right dose, the right monitoring, at the right time — and knowing when the answer is no. That judgment belongs to a veterinarian who has examined your cat, so bring your own vet in before the first dose. The medicine is the easy part; the care around it should adapt as your cat ages.
Start by taking the protocol to your own vet. If your cat is not a candidate, that answer is worth knowing too.
This page is educational and is not veterinary advice. Rapamycin is a prescription medicine; whether to use it is a decision made with a veterinarian who has examined your animal. No medicine is licensed to “extend longevity” — the statements here describe published research and ongoing studies.