Comparison
PT-141 vs TB-500
Side-by-side of PT-141 and TB-500. Every row below is pulled from the compound schema and will update as our data grows. For deeper reads, follow through to each compound page.
PT-141
PT-141 peptide (bremelanotide, Vyleesi): MC4R agonist for libido and erectile dysfunction. 1.75 mg subcutaneous, 30 to 60 min onset, 2 to 4 h half-life.
TB-500
TB-500 peptide, a 17-aa thymosin beta-4 fragment. Preclinical tendon and wound healing via actin sequestration. Typical dosage 2 to 5 mg weekly. No human RCTs.
Effects at a glance
PT-141
- •Cyclic 7-amino-acid synthetic peptide and melanocortin receptor agonist (MC4R-preferring)
- •FDA approved in 2019 as Vyleesi for hypoactive sexual desire disorder in pre-menopausal women
- •Acts centrally on hypothalamic sexual-desire circuits rather than peripherally on vasculature
- •On-demand dosing: subcutaneous 1.75 mg approximately 45 minutes before sexual activity
- •Common adverse effects: nausea (~40%), flushing, headache, injection-site reactions, hyperpigmentation
- •Off-label male ED use is documented but not FDA approved; mechanism is distinct from PDE5 inhibitors
TB-500
- •17-amino-acid fragment of endogenous Thymosin Beta-4, an actin-sequestering peptide
- •Preclinical models show accelerated tendon, ligament, and dermal wound healing
- •Equine veterinary use for soft-tissue injury is the most documented real-world application
- •Anecdotal human protocols use 2 to 5 mg twice weekly subcutaneously for 4 to 6 weeks
- •WADA banned under S2 (peptide hormones, growth factors) since 2018
- •No completed phase II or III human RCTs as of 2026; long-term safety unestablished
Side-by-side
| Attribute | PT-141 | TB-500 |
|---|---|---|
| Category | peptide | peptide |
| Also known as | Bremelanotide, Vyleesi | Thymosin Beta-4 fragment, TB4-Frag, Thymosin Beta 4 |
| Half-life (hr) ↗ | 2.7 | 2 |
| Typical dose (mg) ↗ | 1.75 | 2.5 |
| Dosing frequency | as needed (max once per 24 hours, max 8 per month) | 2x weekly (anecdotal protocols) |
| Routes | subcutaneous | subcutaneous, intramuscular |
| Onset (hr) | 0.75 | - |
| Peak (hr) | 1.5 | - |
| Molecular weight | 1025.18 | 4963.4 |
| Molecular formula | C50H68N14O10 | C212H350N56O78S |
| Mechanism | Synthetic agonist of melanocortin receptors with preference for MC4R, expressed in hypothalamic and limbic circuits regulating sexual motivation. Engages central pathways distinct from peripheral PDE5-mediated vasodilation. | Sequesters G-actin monomers, modulates cell migration and angiogenesis, and upregulates VEGF and myosin transcription. Promotes endothelial differentiation and stem-cell migration to injury sites in preclinical models. |
| Legal status | Prescription only as Vyleesi; FDA-approved 2019 for HSDD in pre-menopausal women. Compounded versions sold off-label for male sexual function are research-use-only grey market. | Not FDA approved; research-use-only grey market; banned by WADA |
| WADA status | allowed | banned |
| DEA / Rx | Rx only (not a controlled substance) for the FDA-approved Vyleesi formulation | Not FDA approved; not scheduled; research-chemical status |
| Pregnancy | Not recommended; contraindicated during pregnancy per Vyleesi label | Insufficient data |
| CAS | 189691-06-3 | 885340-08-9 |
| PubChem CID | 9941379 | 62707662 |
| Wikidata | Q422059 | Q7799921 |
Safety profile
PT-141
Common side effects
- nausea (~40%)
- flushing
- headache
- injection-site reactions
- hyperpigmentation (focal, gums, face, breasts)
- transient blood pressure increase (~6 mmHg systolic)
Contraindications
- uncontrolled hypertension
- established cardiovascular disease
- pregnancy
- naltrexone co-administration (reduces opioid efficacy due to MC receptor crosstalk)
Interactions
- naltrexone (oral): bremelanotide reduces oral naltrexone exposure significantly; avoid co-administration(major)
- antihypertensives: transient BP rise after bremelanotide can offset BP control(moderate)
- PDE5 inhibitors (sildenafil, tadalafil): no documented adverse interaction; mechanisms are non-overlapping(minor)
TB-500
Common side effects
- injection-site irritation
- fatigue (anecdotal)
- lethargy in early dosing (anecdotal)
Contraindications
- pregnancy
- active malignancy (theoretical angiogenic concern)
- no established human safety profile
Interactions
- BPC-157: Frequently co-administered in anecdotal healing protocols; no controlled interaction data(minor)
Which Should You Take?
PT-141 comes out ahead for most readers on the criteria we weight: 2 catalogued goals, research-only / gray-market sourcing, with a Tier-A outcome catalogued. TB-500 is the right call when one of the conditionals below applies.
- → If your priority is sexual function, pick PT-141.
- → If your priority is libido, pick PT-141.
- → If your priority is post-training recovery, pick TB-500.
- → If your priority is tendon repair, pick TB-500.
Edge case: PT-141 is contraindicated in pregnancy; TB-500 is the safer pick if that applies.
Default choice: PT-141. Wider use case, a Tier-A evidence outcome catalogued, and broader goal coverage. Reach for TB-500 only if your priority sits squarely in the goals it owns above.
This verdict is generated from each compound's schema (goals, legal status, evidence outcomes, dosing route). It updates automatically as our compound data evolves; the deeper read sits on each individual compound page.
Common questions
What is the difference between PT-141 and TB-500?
PT-141 and TB-500 differ in category (peptide vs peptide), mechanism, and typical dosing. See the side-by-side table for full details.
Which has a longer half-life, PT-141 or TB-500?
PT-141 half-life is 2.7 hours; TB-500 half-life is 2 hours.
Can you stack PT-141 with TB-500?
Stack compatibility depends on mechanism overlap, legal status, and individual response. Check each compound page for specific interactions and contraindications before combining.
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