Comparison
Urolithin B vs Urolithin A
Anabolic signal vs. mitochondrial cleanup: muscle growth or deep recovery?
Urolithin B
Gut-Derived Polyphenol Metabolite
Urolithin A
Mitophagy Activator
Effectiveness Profile
At a Glance
| Urolithin B | Urolithin A | |
|---|---|---|
| Type | Longevity | Longevity |
| Legal status | Research | OTC |
| Half-life | 17–22 hours (aglycone, class-extrapolated); 25–58 hours (glucuronide conjugates) | ~17–22 hours (glucuronide conjugate); free UA short |
| Preferred route | Oral | Oral |
| Dose frequency | once-daily | once-daily |
| Beginner dose | 50–100 mg | 250–500 mg |
| Intermediate dose | 250–500 mg | 500–1000 mg |
| Advanced dose | 500–1000 mg | 1000–1000 mg |
| Cycle length | 8–16 wks | 8–52 wks |
| Bioavailability | 5% | 15% |
| Time to peak | 6h | 6h |
| Active duration | 24h | 24h |
| Storage | Room temperature, desiccated, protected from light; hygroscopic powder | Room temperature, dry, protected from light |
| PCT required | No | No |
| Ancillaries required | No | No |
| Safe for women | Yes | Yes |
Verdict
Urolithin B wins for: direct muscle hypertrophy signaling via AR/mTORC1, suppressing atrogenes during cuts or immobilization, and stacking cleanly with creatine for recomp-focused protocols. It is the only urolithin with in vivo hypertrophy data and measurable anabolic effects—even if those effects are modest (creatine-range).
Urolithin A wins for: mitochondrial health, endurance, and long-term recovery through clinically validated mitophagy induction. UA is evidence-backed for improving muscle endurance and mitochondrial function in chronic protocols and is the clear leader for longevity or master's protocols where fatigue resistance and organ health are the goals.
Pick A or B?
Pick Urolithin B if:
- The protocol targets muscle mass retention or slow-burn hypertrophy during cuts, TRT, or immobilization
- A non-suppressive, anabolic adjunct is desired without the SARM/PED baggage
- The goal is to suppress muscle atrogenes (MuRF1/atrogin-1) for anti-catabolic effect
- Stacking with creatine, high-protein diets, or minimal-AAS cycles is the plan
- Hands are tied on UA-type mitophagy focus, but muscle signal is wanted
Pick Urolithin A if:
- Deep mitochondrial health and muscle endurance are primary (e.g., high-volume training, master's protocols)
- The priority is long-term recovery support with human RCT and biopsy data
- Stacking for longevity anti-aging (NAD+, rapa, etc.) is core to the protocol
- High baseline fatigue or slow recovery is limiting progression
- The user lacks the gut microbiome for natural dietary conversion and needs direct UA delivery