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Follistatin-34417 residues (approx.)GNCWLRQAKNGRCQVLYEach bubble = one amino acid. Size = residue mass. Color = chemical class.Uses closest standard amino acids for non-standard residues.Also known as: FS-344, FS344, Follistatin 344
Ten out of eleven bodybuilders in a peer-reviewed case series developed retinal damage after injecting this peptide (Sii et al.)[1]. Follistatin-344 (FS-344) is a naturally occurring glycoprotein that traps myostatin and activin, two TGF-beta superfamily proteins that limit skeletal muscle growth. The dramatic numbers (194 to 327 percent muscle mass increases) all come from transgenic mice and AAV gene therapy with continuous expression. Injectable FS-344 has a 90-minute half-life, delivering brief suppression spikes rather than sustained inhibition. Community results remain highly inconsistent, and roughly half of commercial products have tested as mislabeled.
Ten out of eleven bodybuilders developed retinal damage after injecting follistatin-344. That case series (Sii et al., International Ophthalmology)[1] is the most important published safety data for anyone considering this peptide. Follistatin-344 (FS-344) is a glycoprotein that binds and neutralizes myostatin (GDF-8) and activin A, both members of the TGF-beta superfamily. After injection, FS-344 gets cleaved into two active forms: FS-315 circulates in serum, while FS-288 binds tightly to cell surfaces in muscle tissue. Both forms physically trap myostatin before it reaches ActRIIB receptors on muscle cells. The animal research is striking. Haidet and colleagues showed long-term skeletal muscle growth in primates using AAV-delivered follistatin [2]. Gene therapy trials in Becker muscular dystrophy patients improved walking distance without serious adverse events [3]. Those results reflect continuous follistatin expression, not brief pharmacokinetic spikes from daily subcutaneous injection. Community experience is mixed. With fewer than 20 dedicated Reddit threads, follistatin sits in the niche tier. Users who report gains describe acute muscle fullness and modestly improved recovery. Product authenticity dominates the conversation; a 2020 study found roughly 50 percent of commercial FS315/FS344 products were mislabeled. Legitimate recombinant follistatin costs around $4,600 per mg from scientific suppliers. Research peptide vendors sell it for $107 to $160 per mg. That price gap is telling you something. No human randomized controlled trial exists for injectable FS-344. Dosing is extrapolated from primate studies and gene therapy research.
Follistatin operates as a molecular trap within the TGF-beta superfamily signaling network. Its primary target is myostatin (GDF-8). Activin A is the secondary target. Both myostatin and activin normally bind to ActRIIB receptors on the surface of muscle cells. That binding activates SMAD2/3 transcription factors inside the cell. The SMAD2/3 pathway suppresses muscle protein synthesis and blocks satellite cell activation. Follistatin intercepts these ligands before they reach ActRIIB. The binding affinity is high enough that one follistatin molecule neutralizes one myostatin dimer completely. After subcutaneous injection, FS-344 splits into two functional isoforms. FS-315 has moderate heparin-binding affinity and circulates through the bloodstream. FS-288 binds tightly to heparan sulfate proteoglycans on cell surfaces, concentrating effects locally in tissue. The FS-288 form also has stronger potential for FSH suppression because follistatin inhibits activin, which regulates FSH secretion. What makes the animal data unusual is the type of growth. Transgenic mouse studies showed both hypertrophy (larger muscle fibers) and hyperplasia (more fibers). That combination is rare; most anabolic agents produce one or the other. Haidet and colleagues confirmed long-term skeletal muscle gains in primates [2]. The 90-minute circulating half-life is the core limitation. Gene therapy delivers continuous follistatin expression. A daily subcutaneous injection gives a brief spike followed by rapid clearance. Whether repeated transient suppression produces the same downstream signaling as sustained inhibition remains an open question.
No human RCT data for injectable FS-344. Dramatic muscle mass increases (194–327%) are from transgenic mice and AAV gene therapy: continuous overexpression, not daily peptide injections. Brief 90-min pharmacokinetic spikes from SC dosing are pharmacologically distinct from sustained gene therapy expression. The only published human safety signal is a documented CSCR case series (10/11 bodybuilders)[1], subsequently formally incorporated into ophthalmology literature (2025 Survey of Ophthalmology)[4].
Dag et al. 2020, International Ophthalmology (PMID 32671599): CSCR in 11/11 bodybuilders; Haidet et al. 2008 PMC2393740: long-term skeletal muscle enhancement in primates
Zero published human RCTs for injectable FS-344. All efficacy data is animal (transgenic/AAV) or extrapolated from gene therapy trials in DMD/BMD patients. PK half-life (~90 min) makes transient peptide injections pharmacologically unlike gene therapy. No dose-finding studies in humans.
Results are highly inconsistent. Product authenticity is the dominant concern: roughly half of commercial FS344 products were found mislabeled. The subset who report gains describe acute muscle fullness and modestly enhanced recovery rather than dramatic hypertrophy. Awareness of the CSCR/vision risk is growing in experienced communities.
Science and community agree myostatin inhibition is the mechanism and that injectable FS-344 is pharmacologically distinct from gene therapy. They diverge on whether transient daily SC injections produce meaningful muscle gain: community has believers and skeptics; science has no confirmatory human data. The CSCR risk is the one area where published evidence and community awareness are converging.
| Level | Dose / Injection | Frequency |
|---|---|---|
| Beginner | 100mcg | Daily |
| Moderate | 200mcg | Daily |
| Aggressive | 200mcg | Daily |
Reconstitution math for a 1 mg vial with 1.0 mL bacteriostatic water: each 0.1 mL (10 units on a U-100 insulin syringe) equals 100 mcg. Beginner dose is 10 units. Moderate dose is 20 units. Aggressive dose is 30 units. Product authenticity is the thing most beginners miss with this peptide. Around half of commercial FS-344 samples have tested as mislabeled. Real recombinant follistatin runs about $4,600 per mg from scientific-grade suppliers; research vendors sell it for $107 to $160 per mg. That gap should raise questions. Only buy from vendors with independent, batch-specific HPLC or mass spectrometry COAs. Generic certificates from the vendor itself are not verification. Cycle 2 weeks on, 4 weeks off. Daily injection is required because the half-life is only 90 minutes; you can't skip days and expect accumulation. Insulin syringe (29 to 31 gauge) for accuracy at these volumes. Reconstitute by rolling the vial gently. Do not shake. Store reconstituted product at 2 to 8 degrees Celsius and use within 14 days.
Short cycles recommended due to limited long-term safety data. Some protocols extend to 4 weeks on.
Cycling is primarily driven by the absence of long-term human safety data and the CSCR vision risk, which appears to be dose-exposure-dependent (recurrent CSCR in repeat users). A secondary theoretical reason is antibody formation: with repeated injection, the immune system may generate neutralizing antibodies against exogenous follistatin, reducing efficacy over time (no published human data, but documented in analogous protein therapeutics). Activin pathway effects on FSH also warrant periodic hormonal recovery.
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Expected: Modest muscle fullness and potentially enhanced recovery if product is authentic; dramatic hypertrophy unlikely from brief PK spikes alone
Monitor: Baseline retinal exam strongly recommended before use. Report any visual distortion, blind spot, or central blurring immediately: these are CSCR symptoms.
Reconstitute one 1 mg vial with 1.0 mL of bacteriostatic water. Direct the stream down the glass wall, not onto the powder. Swirl gently or roll between your palms. Never shake.
Draw your dose with a U-100 insulin syringe (29 to 31 gauge). Beginner: 10 units = 100 mcg. Moderate: 20 units = 200 mcg. Aggressive: 30 units = 300 mcg.
Pinch a fold of skin on the abdomen or outer thigh.
Insert the needle at a 45-degree angle into the subcutaneous fat layer. Inject slowly and steadily.
Abdomen (at least 2 inches from the navel) and outer thigh are the standard rotation.
Morning or pre-workout is the community preference.
Store the reconstituted vial upright in the refrigerator at 2 to 8 degrees Celsius. Use within 14 days. Lyophilized (unreconstituted) vials store at room temperature up to 30 days, refrigerated up to 12 months, or at -20 degrees Celsius for long-term storage.
Perform an Amsler grid self-check each morning before injecting. Cover one eye, look at the grid at arm's length, check for wavy lines, blind spots, or central distortion. If anything looks off, stop and see an ophthalmologist.
No dose adjustment: 100–200 mcg SC daily is the reference protocol
Use insulin syringe for accuracy at these low doses. Some users report persistent injection site lumps with repeated SC use in the same location: rotate sites rigorously.
Community protocols use same dose range (50–200 mcg) via IM. Lower-dose emerging protocol (50 mcg IM pre-workout) is IM-specific.
IM injection into the trained muscle is reported to reduce injection site reactions. No published pharmacokinetic comparison of IM vs SC for FS-344. Theoretical local concentration advantage is unproven.
Most common FS-344 stack. Combines myostatin pathway inhibition with IGF-1/mTOR-driven protein synthesis. Note: IGF-1 signaling may upregulate endogenous follistatin: additive or redundant effect is unclear.
50–100 mcg IGF-1 LR3 on training days alongside FS-344 cycle
GH secretagogue pairing: adds GH pulse to myostatin inhibition for combined anabolic signaling.
2 mg CJC-1295 DAC 1–2×/week alongside FS-344 daily dosing
GHRP partner for CJC-1295 stack; selectively stimulates GH with minimal cortisol/prolactin. Frequently run as trio with CJC-1295 + FS-344.
100–200 mcg Ipamorelin 2–3×/day alongside FS-344 cycle
Protective stack: BPC-157 added for connective tissue adaptation support. Myostatin inhibition may cause rapid muscle growth that outpaces tendon/ligament strength; BPC-157 theoretically mitigates this risk.
250–500 mcg BPC-157 daily throughout FS-344 cycle and off period
Additive myostatin inhibition: cumulative suppression may produce excessive and unpredictable muscle growth, cardiac risk, and tendon strain. These are experimental compounds with significant safety profiles even alone.
Do not combineCompounded cardiovascular risk: both FS-344 (rapid muscle/cardiac hypertrophy) and AAS (LVH, dyslipidemia) carry cardiovascular load. Combined use substantially elevates cardiac risk.
Compounded anabolic signaling with HPG axis suppression. FS-344 may suppress FSH via activin inhibition; combining with SARMs adds LH/FSH suppression and androgen receptor modulation.
Unpredictable pathway interactions: follistatin works within the TGF-beta superfamily. TGF-beta modulators used clinically for fibrosis could have additive or antagonistic effects.
Pricing updated 2026-04-09
The most documented risk with follistatin-344 injection is central serous chorioretinopathy (CSCR), a condition where fluid accumulates under the retina and distorts central vision. Sii and colleagues published a retrospective case series in International Ophthalmology [1] reporting CSCR in 10 of 11 male bodybuilders after high-dose subcutaneous FS-344 injection. A 2025 Survey of Ophthalmology review [4] formally incorporated this finding into mainstream ophthalmology literature. Repeat users in the case series developed recurrent episodes. Subretinal fluid resolved in approximately 2.3 months for single-injection cases. Anyone with pre-existing retinal disease or a history of CSCR should not use follistatin. Period. Symptoms of CSCR include blurred central vision, blind spots, color distortion, and wavy lines. These can appear during the active cycle or during the off period afterward. A daily Amsler grid self-check takes 60 seconds and catches early signs before damage progresses. Injection site reactions are the most commonly reported community complaint. Redness, swelling, and mild pain at the injection site occur frequently. Persistent subcutaneous lumps happen when users fail to rotate sites. Switching from subcutaneous to intramuscular administration reduces these reactions based on community reports. The safety profile beyond CSCR has large gaps. No long-term studies exist for repeated subcutaneous FS-344 injection in healthy humans. Myostatin is expressed in cardiac tissue; chronic suppression could theoretically affect cardiac muscle remodeling. Rapid skeletal muscle growth may outpace tendon and ligament adaptation. Myostatin-null animal models show brittle tendons relative to muscle mass. Follistatin inhibits activin, which regulates FSH. Extended or repeated use may suppress FSH and affect fertility. FSH and LH blood work after each cycle is recommended for anyone going beyond a single cycle. Target ranges: FSH 1.5 to 12.4 IU/L, LH 1.7 to 8.6 IU/L (men). A 2024 study [5] flagged follistatin's effect on vascular function through activin A inhibition. Baseline cardiovascular assessment (resting ECG, blood pressure) before multi-cycle use is a reasonable precaution. Contraindications: active cancer or history of hormone-sensitive cancers, pregnancy or breastfeeding, cardiac conditions, and children or adolescents (growth plate concerns). Any visual disturbance means immediate cessation and ophthalmology evaluation. Do not wait for the off period.
Verify Follistatin-344 dosing and safety with a second opinion
Follistatin-344 is among the highest-risk peptides for product inauthenticity. A 2020 study found approximately 50% of commercially available FS315/FS344 products were mislabeled. Real recombinant human follistatin costs ~$4,600/mg from scientific suppliers: research-grade peptide vendors sell at $107–160/mg, implying significant production variation. Without mass spectrometry or vendor-specific third-party HPLC COA, the user cannot confirm they have authentic FS-344.
| Test | When | Target |
|---|---|---|
| Retinal examination (OCT or dilated fundus exam) | Before first cycle, after each cycle, and immediately if any visual symptom occurs | No subretinal fluid on OCT; no central vision defects on Amsler grid |
| FSH / LH | Baseline before first use; after each cycle for extended or repeat users | FSH: 1.5–12.4 IU/L (men); LH: 1.7–8.6 IU/L (men) |
| Amsler grid self-check | Daily during active phase: take 60 seconds each morning before injecting | — |
| Cardiovascular assessment (resting ECG, blood pressure) | Baseline and after multi-cycle use | — |
CSCR (central serous chorioretinopathy) documented in 10/11 bodybuilders injecting FS-344 (PMID 32671599). Now formally incorporated in mainstream ophthalmology literature (PMID 39933627, Survey of Ophthalmology 2025). Repeat users develop recurrent CSCR.
Follistatin inhibits activin A/B, which regulates FSH secretion. Prolonged or repeated use may suppress FSH and affect fertility. FS-288 isoform has higher tissue binding and greater potential for FSH suppression; FS-344 is cleaved to FS-288 in vivo.
Inexpensive, at-home screen for early CSCR. Look for wavy lines, blind spots, or central blurring. If positive, stop immediately and seek ophthalmology.
Rapid skeletal muscle hypertrophy can be accompanied by cardiac muscle changes. Myostatin is expressed in cardiac tissue; theoretical risk of cardiac remodeling with prolonged inhibition. Blood pressure: 2024 study (PMID 39300291) shows follistatin affects vascular function via activin A inhibition.
Myostatin binding begins within hours. No visible changes yet.
Myostatin inhibition underway at molecular level. Possible increase in training recovery.
Increased muscle fullness and improved strength reported by users. First cycle ends: begin 4-week off period.
Cumulative gains across multiple cycles. Most noticeable muscle growth if combined with resistance training.
Days 1 through 3: FS-344 begins binding myostatin and activin within hours of injection. Circulating myostatin drops during the roughly 90-minute active window after each dose. Nothing visible changes yet. Some users notice mild redness or warmth at the injection site. Start your daily Amsler grid check from day one. Week 1: Repeated daily injections create brief windows of myostatin suppression. Whether those transient pulses add up to meaningful cumulative inhibition is unproven. Satellite cell activation is theoretically beginning at the molecular level. Some users describe modest improvement in muscle fullness or training recovery. The majority notice no visible change. Keep monitoring for injection site reactions and any visual disturbances. Week 2, end of standard cycle: The most variable phase. A minority of users report muscle fullness or scale weight increases of 5 to 15 pounds. Most see modest or no measurable change. Extraordinary weight claims likely include glycogen loading and water retention, not actual new muscle tissue. No sustained myostatin suppression is expected given the 90-minute half-life. The first 2-week cycle ends; begin the 4-week off period. Off period, weeks 3 through 6: Myostatin and activin levels normalize within days after the last injection. Any genuine hypertrophic gains (new myofibers) should be maintained with continued resistance training. Muscle fullness often fades as glycogen and water shifts normalize. CSCR subretinal fluid can first become symptomatic during the off period, not only during active dosing. A post-cycle retinal exam is recommended. Cycles 2 through 3, week 7 onward: No published data exists on cumulative effects of injectable FS-344 across multiple cycles in humans. Antibody formation against exogenous follistatin is a theoretical risk after repeated exposure, though no human data confirms this. Users in the CSCR case series who injected repeatedly developed recurrent retinal episodes. Product authenticity remains the confounding variable across all cycles.
FS-344 binds myostatin and activin within hours. Circulating myostatin levels measurably reduced during the ~90-min active window post-injection.
No perceptible changes. Some report mild injection site redness or warmth.
Repeated brief myostatin suppression pulses. Whether cumulative inhibition approximates sustained suppression is unproven. Satellite cell activation theoretically beginning.
Possible modest increase in muscle fullness and pumps. Enhanced recovery between training sessions. Majority report no visible change.
Continued transient myostatin inhibition. No sustained suppression expected given half-life. Some users may report glycogen/water retention shifts presenting as muscle fullness.
The most variable phase. A minority report significant muscle fullness or scale weight increases (5–15 lbs). Most see modest or no change. Extraordinary claims likely include glycogen loading and water retention.
Myostatin and activin levels normalize within days after cessation. Any hypertrophic gains are maintained through training; no expectation of gains accumulating during off period.
Muscle fullness often fades. Genuine hypertrophic gains (new myofibers) would be maintained with continued training. Watch for CSCR symptoms: retinal fluid can manifest during or after the cycle.
No published data on cumulative FS-344 injectable effects in humans across cycles. Antibody formation to follistatin after repeated exposure is a theoretical risk (no human data).
Cumulative gains reported by some with concurrent resistance training and caloric surplus. Product authenticity remains the confounding variable across all cycles. Repeat injection users in CSCR case series developed recurrent retinopathy.
Source: Estimated from PK modeling; FS-344 circulating half-life ~90 minutes
Loading the interactive decay curve.
Follistatin-344 has no FDA approval for any indication. It is classified as a research-only compound. Injectable FS-344 is sold by peptide research vendors under "for research use only" labeling. No compounding pharmacy pathway exists for this peptide in the United States. Gene therapy applications of follistatin (AAV-delivered) have been studied in clinical trials for muscular dystrophy under FDA-authorized IND protocols. Those trials used a completely different delivery method and regulatory pathway from the injectable peptide form. WADA lists myostatin inhibitors under category S2 (growth factors and growth factor modulators) as prohibited substances. Athletes subject to anti-doping testing should not use follistatin-344. No pending regulatory changes affecting follistatin-344 availability were identified as of April 2026. The compound remains in the research chemical category. This content is for informational purposes only. It does not constitute medical advice. Consult a qualified healthcare provider before using any research compound.
Peptide Schedule Research TeamReviewed Apr 20266 Citations
