Follistatin 315
FST-315 · FST315 · circulating follistatin
The circulating splice of follistatin (315 aa) versus FST-344, which we already list. FST-315 carries the acidic C-terminal tail that keeps it in plasma; FST-344 is the tissue-associated form. Gray-market vials labeled 315 vs 344 are isoform SKUs of the same myostatin/activin-binding protein — not two drugs. Neither is ACE-031 (a discontinued ActRIIB fusion).
Mechanism of Action
Follistatin-315 is the circulating splice (acidic C-terminal tail). Follistatin-344 is the tissue-associated form we already list. Both bind myostatin and activins at ActRIIB. Gray-market “315” vs “344” vials are isoform SKUs — identity is often unverified.
ACE-031 / ramatercept was a different molecule (ActRIIB fusion), discontinued. Do not treat FST-315 as that program.
Source: Follistatin biology PMID: 17108139; isoform distinction is splice-form biochemistry, not a 315-specific human trial
Isoform, not a new drug
315 vs 344 changes where the protein hangs out more than what it binds. WADA treats myostatin inhibitors as S4. Research powder is not a clinical myostatin drug.
Dosing Protocol
| Typical Dose | 100-300 mcg/day (research; same ballpark as FST-344 community use) |
| Frequency | 1× daily for short research cycles |
| Half-Life | ~hours (circulating isoform; human peptide-SKU PK unpublished) |
| Common Vial Sizes | 1 mg |
Dosing Protocols
Research (community, unlabeled)
Body-Weight Dosing Reference
Estimated doses extrapolated from the published research range of 100–300 mcg/day (referenced to 70 kg / 154 lb). These are approximations — consult a qualified healthcare provider for personalised guidance.
| Weight | Low Dose | Target Dose | High Dose |
|---|---|---|---|
| 120 lb(54 kg) | 77 mcg | 154 mcg | 231 mcg |
| 140 lb(63 kg) | 90 mcg | 180 mcg | 270 mcg |
| 160 lb(73 kg) | 104 mcg | 209 mcg | 313 mcg |
| 180 lb(82 kg) | 117 mcg | 234 mcg | 351 mcg |
| 200 lb(91 kg) | 130 mcg | 260 mcg | 390 mcg |
| 220 lb(100 kg) | 143 mcg | 286 mcg | 429 mcg |
| 250 lb(113 kg) | 161 mcg | 323 mcg | 484 mcg |
💉 For exact syringe units based on your vial concentration, use the Follistatin 315 Reconstitution Calculator →
Administration
Expected Timeline
Who Is It For?
Isoform identity
LowListed so 315 search does not 404. Prefer the 344 leaf for the class story; this page is the circulating splice.
Reconstitution Example
Safety & Considerations
Myostatin/activin blockade is not a casual recovery peptide. Theoretical fertility, vascular, and off-target TGF-β effects. WADA S4. Research-only.
Regulatory & Legal Status
Circulating follistatin isoform. Not ACE-031. No FDA myostatin-inhibitor approval
Competitive athletes subject to anti-doping controls should not use Follistatin 315.
Research Chemical
US Compounding: Not eligible / not available
⚠️ This information is for educational purposes only and may not reflect the most current regulatory updates. Always verify with official FDA, WADA, and jurisdiction-specific sources before use.
Follistatin 315 vs. Follistatin 344
| Attribute | Follistatin 315 | Follistatin 344 |
|---|---|---|
| Isoform | Circulating (acidic C-tail) | Tissue-associated splice |
| Ligands | Myostatin / activins (same class) | Myostatin / activins (same class) |
| SKU reality | Often unverified gray-market powder | Same problem |
Verdict: 315 vs 344 is splice localization, not two mechanisms. Neither is ACE-031.
Dosing Quick Reference
Frequently Asked Questions
Is 315 stronger than 344?▼
Is this ACE-031?▼
References
- Lee SJ et al. lineage “Follistatin / myostatin biology (class).” PNAS / related (2007). PMID: 17108139
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