Comparison
PT-141 vs Thymosin Alpha-1
Side-by-side of PT-141 and Thymosin Alpha-1. 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.
Thymosin Alpha-1
Thymosin alpha-1 peptide (Zadaxin, thymalfasin): 28-amino-acid TA1 immunomodulator. Dosing, T-cell effects, hepatitis B and HCV adjunct evidence.
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
Thymosin Alpha-1
- •28-amino-acid synthetic peptide identical to thymic-derived immunomodulator
- •Approved in over 35 countries as Zadaxin for hepatitis B, hepatitis C adjunct, and immune support
- •Not FDA approved in US; compounded by 503A/503B pharmacies for off-label immune support
- •Modulates T-cell maturation, NK activity, and Th1 polarization in immunocompromised states
- •Standard label dose: 1.6 mg subcutaneously twice weekly
- •Cleanest safety profile in the peptide class with hundreds of regulated trials behind it
Side-by-side
| Attribute | PT-141 | Thymosin Alpha-1 |
|---|---|---|
| Category | peptide | peptide |
| Also known as | Bremelanotide, Vyleesi | Talpha1, Ta1, Zadaxin, Thymalfasin |
| Half-life (hr) ↗ | 2.7 | 2 |
| Typical dose (mg) ↗ | 1.75 | 1.6 |
| Dosing frequency | as needed (max once per 24 hours, max 8 per month) | 2x weekly |
| Routes | subcutaneous | subcutaneous, intramuscular |
| Onset (hr) | 0.75 | 24 |
| Peak (hr) | 1.5 | 168 |
| Molecular weight | 1025.18 | 3108.32 |
| Molecular formula | C50H68N14O10 | C129H215N33O55 |
| 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. | Synthetic peptide modulator of innate and adaptive immunity. Promotes T-cell maturation and CD4/CD8 production, modulates Th1/Th2 balance, stimulates NK cell activity, and modulates TLR2/TLR9 signaling in dendritic cells. |
| 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. | Approved in 35+ countries as Zadaxin (hepatitis B, hepatitis C adjunct, immune support); not FDA approved in US; compounded by 503A/503B pharmacies for off-label use; not on WADA Prohibited List |
| WADA status | allowed | unknown |
| DEA / Rx | Rx only (not a controlled substance) for the FDA-approved Vyleesi formulation | Rx only via international approval or US compounding (no controlled-substance schedule) |
| Pregnancy | Not recommended; contraindicated during pregnancy per Vyleesi label | Not recommended; insufficient data |
| CAS | 189691-06-3 | 62304-98-7 |
| PubChem CID | 9941379 | 16130571 |
| Wikidata | Q422059 | Q913854 |
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)
Thymosin Alpha-1
Common side effects
- mild injection-site irritation (rare)
- transient mild fatigue (rare)
- occasional headache (rare)
Contraindications
- pregnancy
- lactation
- active organ transplant rejection therapy
- systemic immunosuppression for autoimmune disease (relative)
- severe active autoimmune disease (caution)
Interactions
- interferon-alpha: additive immune effect; used clinically in approved combination protocols(minor)
- calcineurin inhibitors (cyclosporine, tacrolimus): theoretical destabilization of immunosuppression; avoid(major)
- antimetabolites (azathioprine, mycophenolate): theoretical destabilization of immunosuppression; avoid(major)
- vaccine administration: may augment vaccine response in elderly or immunocompromised; coordinate with clinician(minor)
Which Should You Take?
Thymosin Alpha-1 comes out ahead for most readers on the criteria we weight: 3 catalogued goals, Approved in 35+ countries as Zadaxin (hepatitis B, hepatitis C adjunct, immune support); not FDA approved in US; compounded by 503A/503B pharmacies for off-label use; not on WADA Prohibited List, with a Tier-A outcome catalogued. PT-141 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 immune support, pick Thymosin Alpha-1.
- → If your priority is post-training recovery, pick Thymosin Alpha-1.
Edge case: PT-141 is contraindicated in pregnancy; Thymosin Alpha-1 is the safer pick if that applies.
Default choice: Thymosin Alpha-1. Wider use case, a Tier-A evidence outcome catalogued, and broader goal coverage. Reach for PT-141 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 Thymosin Alpha-1?
PT-141 and Thymosin Alpha-1 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 Thymosin Alpha-1?
PT-141 half-life is 2.7 hours; Thymosin Alpha-1 half-life is 2 hours.
Can you stack PT-141 with Thymosin Alpha-1?
Stack compatibility depends on mechanism overlap, legal status, and individual response. Check each compound page for specific interactions and contraindications before combining.
Go deeper