Sirolimus, Rapamune and Rapamycin: Same Drug, Three Names
A person who has read about rapamycin, been prescribed sirolimus, and collected a box marked Rapamune could be forgiven for thinking three drugs were involved. There is one. The three names belong to different stages of the molecule's life — discovery, regulation, and marketing — and once that is clear, the more useful question comes into view: which form of the one drug you are actually taking, because that does vary, and it matters.
The main page covers the drug itself. This page is the naming and the supply.
Three names, one molecule
Rapamycin is the discovery name. The compound was isolated in the early 1970s from a soil bacterium collected on Easter Island — Rapa Nui to its inhabitants — and named for the place. It is the name the research literature uses, the name the longevity field uses, and the name most people search.
Sirolimus is the drug's official generic name — its International Nonproprietary Name — assigned when it was developed as a medicine. Every prescription, every pharmacy label and every regulatory document uses it. If your prescription says sirolimus, it is rapamycin.
Rapamune is the brand name under which Pfizer (originally Wyeth) sells sirolimus, approved by the FDA in 1999 to prevent organ rejection after kidney transplant, and later for a rare lung disease. It comes as tablets and as an oral solution.
So: one molecule, discovered as rapamycin, regulated as sirolimus, sold as Rapamune. The mTOR protein it inhibits was named after it — the mechanistic target of rapamycin — which is why the drug's name outlived its rebranding.
Generic sirolimus
Rapamune's patents have expired and generic sirolimus tablets have been available in the United States for over a decade, from several manufacturers. They are approved on bioequivalence to Rapamune — the same drug, delivered at the same rate — and they are what most transplant patients, and most longevity users with a prescription, actually take.
One point specific to this drug: sirolimus has a narrow therapeutic window in transplant use, where too little means rejection and too much means toxicity, and transplant physicians have historically been cautious about switching patients between manufacturers. For intermittent longevity use, at far lower exposure and with no rejection to prevent, that caution matters much less — but it is the reason a pharmacist may mention the brand, and the reason we prefer that a person stay on one product rather than alternating.
Generic sirolimus is an FDA-approved manufactured drug. That distinction is the whole of the next section.
Why compounded rapamycin exists
A search for rapamycin online turns up compounded versions — capsules or tablets made to order by a compounding pharmacy — sold by longevity clinics and telehealth companies. Given that an approved generic exists, why?
Partly history: before longevity use was common, generic sirolimus was expensive and insurers would not cover off-label prescriptions, so compounding pharmacies made a cheaper version. Partly form: compounders can make strengths and combinations the generic does not come in. And partly commerce: a compounded product is proprietary to the clinic that sells it, in a way a generic tablet is not.
The problems are real. Sirolimus is poorly soluble and awkward to absorb, and Rapamune's formulation was engineered around that; a compounded capsule is not, and a study comparing compounded rapamycin with the approved product found that the compounded version delivered substantially less of the drug into the blood — meaning a person on compounded rapamycin may be getting a fraction of what the label implies. And under federal law a compounding pharmacy may not make what is essentially a copy of a commercially available drug unless there is a clinical reason the approved product cannot be used — a rule that compounded rapamycin sits uneasily against.
What ACT 2 dispenses
Generic sirolimus tablets — the FDA-approved manufactured drug, dispensed as manufactured, from a licensed pharmacy. We do not use compounded rapamycin, for the three reasons above: the approved product exists, its absorption is characterized and the compounded product's is not, and the regulatory basis for compounding a copy of an available drug is thin.
That makes rapamycin one of the few things on this site that is not a compounded product, and the disclosure line that accompanies compounded medications does not apply to it. What does apply is the off-label statement: sirolimus is approved for transplant and for a rare lung disease, not for longevity, and every prescription we write for it is off-label, with the evidence and the caveats on the main page.
Frequently asked questions
Yes. Rapamycin is the discovery name, sirolimus is the official generic name, Rapamune is Pfizer's brand. One molecule.
It is approved on bioequivalence — same drug, same delivery rate — and is what most patients take. Transplant physicians prefer patients not to switch between manufacturers because of the narrow therapeutic window there; for intermittent longevity use that matters much less, but staying on one product is sensible.
Rapamycin made to order by a compounding pharmacy rather than the approved manufactured tablet. A comparison study found compounded versions delivered substantially less drug into the blood than the approved product.
No. We dispense generic sirolimus tablets, the FDA-approved manufactured drug.
It was discovered and named in the 1970s, given the generic name sirolimus when developed as a medicine, and branded Rapamune at approval in 1999. The protein it targets, mTOR, was named after the drug.
Sirolimus is FDA-approved to prevent transplant rejection and for a rare lung disease. Its use for longevity is off-label.
Where this fits in your plan
The Rapamycin page covers the drug and whether it fits; this page is what arrives in the box. The longevity overview covers where it sits among the options and what it costs to run properly.
We measure first. Then we act.
References
- Rapamune (sirolimus) prescribing information — Pfizer. Approval history: 1999 (renal transplant), 2015 (lymphangioleiomyomatosis).
- FDA. Orange Book: Approved Drug Products with Therapeutic Equivalence Evaluations — sirolimus tablets.
- Vézina C, Kudelski A, Sehgal SN. Rapamycin (AY-22,989), a new antifungal antibiotic. Journal of Antibiotics 1975;28:721–726.
- FDA. Compounded drug products that are essentially copies of a commercially available drug product under section 503A — guidance for industry, 2018.
- Mannick JB, Lamming DW. Targeting the biology of aging with mTOR inhibitors. Nature Aging 2023;3:642–660.
- Back toRapamycin
- Rapamycin mouth ulcersMouth ulcers are the side effect rapamycin users report most. Why mTOR inhibitors cause them, how common they are in longevity use, what helps, and when they mean stopping.Read
- Rapamycin, infections and vaccinesRapamycin is an immunosuppressant at transplant doses and something stranger at the doses longevity users take. What the flu-vaccine paradox showed, the live-vaccine rule, and what to do when you get sick.Read
- Rapamycin for womenA Columbia pilot suggested rapamycin may slow ovarian aging. What the mouse data showed, what the VIBRANT trial actually found, why it is early, and what a woman over 45 should make of it.Read
How we write and review our content
ACT 2 Health provides clinician-led care. Treatments are available only to eligible patients following clinical evaluation and within applicable regulations. This content is educational and is not medical advice. Individual results vary.
Care is delivered via telemedicine by healthcare professionals licensed in the state where the patient is located. Services are available only in states where our providers are licensed.