Head to head
Urolithin A against Urolithin B
Urolithin B is sold on urolithin A's reputation. Urolithin A has human trials showing improved muscle function in older adults; urolithin B's muscle result is C2C12 cells and mice given 10 micrograms a day through an implanted osmotic pump for 28 days.
Column A
Urolithin AUrolithin A
A gut-derived compound that triggers mitophagy and has improved muscle function in older adults in human trials, one of the better-evidenced longevity supplements.
Column B
Urolithin BUrolithin B, gut microbial metabolite of ellagitannins
Sold on the reputation of urolithin A, which has human trials. Urolithin B has none: the muscle result is C2C12 cells and mice given 10 micrograms a day through an implanted osmotic pump for 28 days.
Side by side, on the facts we can check
| Attribute | Urolithin A | Urolithin B |
|---|---|---|
| Category | Muscle & Performance | Muscle & Performance |
| FDA status | Sold as a supplement (GRAS); not an approved drug | Not an approved drug. Sold as a supplement ingredient and as a research chemical. No registered human trial has administered it. |
| Half-life | Several hours | Not established in humans. No human pharmacokinetic study of administered urolithin B exists. |
| Molecular weight | 228.2 Da | 212.2 Da |
| Mechanism | Induces mitophagy, clearing damaged mitochondria and improving the quality of the cellular energy supply, especially in muscle. | In muscle cells and mice, an increase in protein synthesis with repression of the ubiquitin-proteasome degradation pathway, with the androgen receptor implicated genetically and pharmacologically and crosstalk to mTORC1 signalling, possibly through AMPK. This is a different proposed mechanism from urolithin A, which is sold and studied as a mitophagy activator. Which urolithins a person produces from dietary ellagitannins depends on their gut microbiota, and the metabotype categories described in the polyphenol literature differ in whether urolithin A, urolithin B or the isourolithins dominate. |
| Human studies cited | 3 | 1 |
| Legal status, US | Sold as a dietary supplement | Sold as a supplement |
Frequently asked questions
What is the difference between Urolithin A and Urolithin B?
Urolithin A: A gut-derived compound that triggers mitophagy and has improved muscle function in older adults in human trials, one of the better-evidenced longevity supplements. Urolithin B: Sold on the reputation of urolithin A, which has human trials. Urolithin B has none: the muscle result is C2C12 cells and mice given 10 micrograms a day through an implanted osmotic pump for 28 days.
Which has stronger research evidence, Urolithin A or Urolithin B?
This database does not grade compounds. It counts what was run in people: 3 of the 3 studies cited on the Urolithin A profile were human work, against 1 of 4 for Urolithin B. Those counts are of our own citation lists and understate any larger literature, and neither is a recommendation.
Are Urolithin A and Urolithin B FDA-approved?
Urolithin A: Sold as a supplement (GRAS); not an approved drug. Urolithin B: Not an approved drug. Sold as a supplement ingredient and as a research chemical. No registered human trial has administered it..
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.