Healing & Recovery

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).

Not FDA-approved - research chemicalWADA (S4) - prohibited in sport at all times

Quick answer

What it is: The circulating splice of follistatin (315 aa) versus FST-344, which we already list.

Typical research dose: 100-300 mcg/day (research; same ballpark as FST-344 community use)

Reconstitution calculator ↓

Research summary, not medical advice.

Reviewed by Kymata Health Editorial Team

·Last updated: August 2026·Evidence: Low

Typical research dose

100-300 mcg/day (research; same ballpark as FST-344 community use)

Frequency

1× daily for short research cycles

Half-life

Hours-class circulating protein (SKU PK unpublished)

Common vials

1 mg

CAS

N/A (isoform SKU)

Molecular weight

~31–35 kDa class (glycoprotein)

Use-case scores

0–10 against the evidence we have, not a gym ranking. Hidden domains do not apply here.

Muscle / recomp3.5/10
Same ligand class as FST-344. Score tracks that leaf. Isoform SKU is not a second, higher score.

Compound card

Sequence: FST-315 (circulating splice)
Class: Myostatin/activin-binding glycoprotein isoform (not ACE-031, not a second drug vs 344)
Formula: Follistatin isoform 315
Status: Not FDA-approved · research use

Dose it

1 mg + 1 mL BAC water → 1 mg/mL · 100 mcg ≈ 10 units (U-100)

Open in calculator

How it works

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; 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.

Research Use Cases

✓Isoform identity: Low

Dosing

Phase	Dose	Frequency	Notes
Research (community, unlabeled)	100–300 mcg/day	Short cycles	Copied from FST-344 forums. Not a label. Myostatin-inhibitor risk profile.

Administration

Route / form

Subcutaneous (research)

Timing

Not established.

Empty stomach?

No - Food timing is not critical.

Timeline

Unknown in humans

No honest consumer timeline. Muscle-wasting drug programs are not this vial.

Who it is for

Isoform identity

Low

Listed so 315 search does not 404. Prefer the 344 leaf for the class story; this page is the circulating splice.

Reconstitution

Vial	Water	Concentration	Example dose
1 mg	1.0 mL BAC	1 mg/mL	100 mcg = 0.10 mL = 10 units. Same math as 344. Confirm the isoform on the COA.

Change vial size or water volume? Open the reconstitution calculator.

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

FDA Status (US)

Research Only

Circulating follistatin isoform. Not ACE-031. No FDA myostatin-inhibitor approval

WADA Status (2026)

Prohibited (S4)

Competitive athletes subject to anti-doping controls should not use Follistatin 315.

Classification

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.

Limits of current evidence

No 315-specific human trial of gray-market vials.
Identity vs 344 is often unverified on COAs.
ACE-031 / ramatercept was ActRIIB-Fc, discontinued, not this protein.

Verdict

FST-315 is the circulating splice, not a new myostatin drug. Read the 344 leaf for the class story. ACE-031 was a different molecule. WADA S4.

Interactions & Contraindications

Myostatin/activin blockade is not a casual recovery peptide. Theoretical fertility, vascular, and off-target TGF-β effects. WADA S4. Research-only.

Follistatin 315 vs. Follistatin 344

Canonical comparison: 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.

Frequently Asked Questions

Is 315 stronger than 344?▼

It is the circulating isoform. “Stronger” is vendor copy. Ligand class is the same.

Is this ACE-031?▼

No. ACE-031 was an ActRIIB-Fc fusion, discontinued. Different molecule.

How do I reconstitute a 1 mg vial?▼

Same as 344: 1.0 mL BAC → 1 mg/mL. 100 mcg is 10 units. Confirm the isoform first.

WADA?▼

S4. Not a recovery loophole.

Prescription options: compare licensed telehealth providers

Some peptide therapies are available only by prescription after a consult with a licensed clinician.

Compare telehealth →

← Back to Peptide Library