Comparison
Sermorelin vs Thymosin Alpha-1
Side-by-side of Sermorelin 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.
Sermorelin
Sermorelin peptide therapy uses a 29-amino-acid GHRH analog to raise endogenous GH. Dosing, half-life, sermorelin vs ipamorelin, and safety.
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
Sermorelin
- •Synthetic 29-amino-acid GHRH fragment; FDA approved 1997 for pediatric GH deficiency as Geref
- •Voluntarily discontinued by Serono in 2008 for commercial reasons; not safety-related
- •Compounded by 503A/503B pharmacies for off-label adult anti-aging and body-composition use
- •Produces physiologic pulsatile GH release; ~10 to 20 minute plasma half-life
- •Standard anti-aging clinic protocol: 200 to 500 mcg subcutaneously pre-bed, often with ipamorelin
- •Banned by WADA under S2 (peptide hormones, growth factors)
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 | Sermorelin | Thymosin Alpha-1 |
|---|---|---|
| Category | peptide | peptide |
| Also known as | Sermorelin acetate, GRF 1-29, Geref, GHRH (1-29) NH2 | Talpha1, Ta1, Zadaxin, Thymalfasin |
| Half-life (hr) ↗ | 0.25 | 2 |
| Typical dose (mg) ↗ | 0.3 | 1.6 |
| Dosing frequency | 1-2x daily | 2x weekly |
| Routes | subcutaneous | subcutaneous, intramuscular |
| Onset (hr) | 0.25 | 24 |
| Peak (hr) | 0.5 | 168 |
| Molecular weight | 3357.88 | 3108.32 |
| Molecular formula | C149H246N44O42S | C129H215N33O55 |
| Mechanism | Synthetic 29-amino-acid GHRH fragment that binds the GHRH receptor on pituitary somatotrophs to stimulate endogenous pulsatile GH synthesis and release while preserving the GH-IGF-1 negative feedback loop. | 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 | FDA approved 1997 (Geref, pediatric GHD); voluntarily discontinued by Serono 2008; compounded by 503A/503B pharmacies for off-label adult use; banned by WADA | 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 | banned | unknown |
| DEA / Rx | Rx only via compounding (no controlled-substance schedule) | Rx only via international approval or US compounding (no controlled-substance schedule) |
| Pregnancy | Category C (historical labeling); not recommended in pregnancy | Not recommended; insufficient data |
| CAS | 86168-78-7 | 62304-98-7 |
| PubChem CID | 16129617 | 16130571 |
| Wikidata | Q416620 | Q913854 |
Safety profile
Sermorelin
Common side effects
- injection-site pain or irritation
- transient flushing
- headache
- vivid dreams (pre-bed dosing)
Contraindications
- pregnancy
- active malignancy
- history of pituitary tumor
- diabetic retinopathy (theoretical)
- untreated hypothyroidism
Interactions
- ipamorelin: synergistic GH release via parallel GHRH and ghrelin pathways; standard anti-aging clinic pairing(minor)
- CJC-1295: pharmacologically redundant (both GHRH-pathway); typically not stacked(minor)
- insulin: sustained GH can blunt insulin sensitivity over weeks(moderate)
- corticosteroids: blunt GH response; reduce expected efficacy(moderate)
- levothyroxine (untreated hypothyroidism): untreated hypothyroidism blunts GH response; correct thyroid first(moderate)
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?
Sermorelin and Thymosin Alpha-1 score evenly on the criteria we weight (goal breadth, legal accessibility, evidence depth). The conditionals below should drive the decision more than any aggregate score.
- → If your priority is growth-hormone axis, pick Sermorelin.
- → If your priority is healthspan extension, pick Sermorelin.
- → If your priority is immune support, pick Thymosin Alpha-1.
- → If your priority is antiviral action, pick Thymosin Alpha-1.
Edge case: Half-lives differ materially (Sermorelin ~0.25 hr vs Thymosin Alpha-1 ~2 hr). Thymosin Alpha-1 reaches steady state faster; Sermorelin is easier to dial in if tolerability is uncertain.
Default choice: either is defensible. Sermorelin edges out on goal breadth + legal accessibility; Thymosin Alpha-1 is the right call if your priority sits in the goals listed 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 Sermorelin and Thymosin Alpha-1?
Sermorelin 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, Sermorelin or Thymosin Alpha-1?
Sermorelin half-life is 0.25 hours; Thymosin Alpha-1 half-life is 2 hours.
Can you stack Sermorelin 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.
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