No — closely related, but not the same molecule. Sirolimus is rapamycin (same drug, two names). Everolimus (brand names include Afinitor and Zortress) is a semi-synthetic derivative of sirolimus — a "rapalog" — with one chemical modification (a 2-hydroxyethyl group at position 40) that gives it better oral bioavailability and a shorter half-life, making it easier to dose predictably for cancer treatment. Both share the same core mechanism: binding FKBP12 and allosterically inhibiting mTORC1.
Everolimus works the same way sirolimus does — it's why the Atlas's systematic review of aging-relevant mTOR-inhibitor trials covers both together as one drug class.
Despite the shared mechanism, everolimus has been studied far more extensively than sirolimus in oncology specifically — it has 14 studies in the Atlas, 11 of them direct human trials, versus fewer human oncology trials for sirolimus itself.
The two drugs aren't interchangeable in clinical practice, even though they share a mechanism: sirolimus is mainly used for transplant immunosuppression (its original, longest-standing indication) and is the molecule almost all the aging/longevity mouse and human trials in this Atlas actually test. Everolimus is mainly used in oncology and for tuberous sclerosis complex, where its more predictable pharmacokinetics matter for precise dosing against tumors.
