Head to head
Rapamycin against 17-alpha-estradiol
Two compounds that reliably extend mouse lifespan in the same multi-site programme, and one of them only in males. 17-alpha-estradiol does not work in females and nobody knows why, which is the sort of detail that disappears when results are summarised as lifespan extension.
Column A
RapamycinRapamycin (Sirolimus, mTOR inhibitor)
An FDA-approved mTOR inhibitor that extends lifespan in animals and is widely studied off-label at low, intermittent doses for longevity.
Column B
17-alpha-estradiol17-alpha-estradiol, non-feminising estradiol stereoisomer
One of the most reliably replicated lifespan extenders in mice, robust at higher doses and even when started late in life. It does not work in females, and nobody knows why.
Side by side, on the facts we can check
| Attribute | Rapamycin | 17-alpha-estradiol |
|---|---|---|
| Category | Longevity | Longevity |
| FDA status | FDA-approved (Rapamune); longevity use is off-label and investigational | Not approved in the United States for any indication. Marketed in some European countries as a topical preparation for androgenetic alopecia, which is a different use, route and dose from the lifespan work. |
| Half-life | ~60 hours | Not asserted for the mouse dosing regimen. It is fed in the diet in these studies, so exposure is continuous rather than pulsed. |
| Molecular weight | 914.2 Da | 272.4 Da. A steroid, not a peptide. |
| Mechanism | Inhibits the mTOR pathway, mimicking aspects of caloric restriction and enhancing autophagy and cellular maintenance. | The stereoisomer of 17-beta-estradiol at carbon 17, which drops its affinity for classical estrogen receptors by orders of magnitude and removes the feminising activity. Because it is not acting as a conventional estrogen, the mechanism behind its lifespan effect is genuinely unresolved. Reported effects include reduced hypothalamic inflammation, improved hepatic insulin sensitivity, reduced mTOR signalling in liver, and changes in markers of metabolic health. The sex specificity is central to the puzzle: if the compound worked through a non-hormonal metabolic route, there is no obvious reason it should not work in females, and it does not. |
| Human studies cited | 2 | 0 |
| Legal status, US | FDA-approved (for its labeled use), prescription only | Not approved; research use only |
Frequently asked questions
What is the difference between Rapamycin and 17-alpha-estradiol?
Rapamycin: An FDA-approved mTOR inhibitor that extends lifespan in animals and is widely studied off-label at low, intermittent doses for longevity. 17-alpha-estradiol: One of the most reliably replicated lifespan extenders in mice, robust at higher doses and even when started late in life. It does not work in females, and nobody knows why.
Which has stronger research evidence, Rapamycin or 17-alpha-estradiol?
This database does not grade compounds. It counts what was run in people: 2 of the 3 studies cited on the Rapamycin profile were human work, against 0 of 4 for 17-alpha-estradiol. Those counts are of our own citation lists and understate any larger literature, and neither is a recommendation.
Are Rapamycin and 17-alpha-estradiol FDA-approved?
Rapamycin: FDA-approved (Rapamune); longevity use is off-label and investigational. 17-alpha-estradiol: Not approved in the United States for any indication. Marketed in some European countries as a topical preparation for androgenetic alopecia, which is a different use, route and dose from the lifespan work..
Related posts
Blog articles that cover Rapamycin or 17-alpha-estradiol, newest first.
- Longevity / Sep 8, 2026 / 12 minPeptides for Longevity: What the Evidence Actually Shows in 2026
- Longevity / Sep 8, 2026 / 9 minSenolytics in 2026: Dasatinib plus Quercetin, Fisetin, and What Human Trials Have Shown
- Longevity / Sep 8, 2026 / 9 minThe Rapamycin Dosing Debate: What PEARL Tested, the Bioavailability Problem, and What Is Unproven
Reviewed Sep 2026. This page sets two published records side by side. It is educational, it is not medical advice, and it contains no dosing protocols or recommendations for personal use.