At a glance
Effects
- Muscle hypertrophy: Removes myostatin-mediated growth constraints on skeletal muscle, enabling fibre size increases and satellite-cell-driven hyperplasia beyond normal genetic limits [4][3].
- Muscle regeneration / recovery: Animal and early human gene-therapy studies suggest enhanced muscle regeneration potential and improved function in dystrophic muscle [9][3].
- Anti-fibrotic effect: Preclinical data indicate follistatin inhibits muscle fibrosis partly via Smad and AKT signalling pathways [5].
- FSH suppression: By antagonising activin at the pituitary, follistatin reduces FSH secretion, with documented suppression up to 75% in some reports — relevant to fertility [10][8].
- Appetite change: Some users report increased appetite, possibly related to systemic TGF-β pathway modulation; long-term significance is unknown [8].
Glycoprotein peptide / TGF-β antagonist
~1–4 h (exogenous protein; endogenous FS-315 ~10–15 h)
Subcutaneous or intramuscular injection (research use only)
Not approved — investigational gene-therapy only
Very limited — gene-therapy trials only; no peptide-injection RCTs
About Follistatin
Every point here is drawn from public medical and harm-reduction sources. A bracketed number after a claim — like [1]— is a reference: tap it to open the exact source it's based on (numbered list at the bottom). It is not a rating or score. Educational information, not medical advice.
Product specifics
- Est. delivery
- 3–7 business days · EU tracked
Product details as stated by the vendor (claims, not independently verified). Delivery is our standard EU estimate.
What it is
Follistatin (isoforms FS-344 and FS-315) is a naturally occurring glycoprotein peptide that acts as the body's primary inhibitor of myostatin and activin, two TGF-β superfamily members that limit muscle growth [1][2]. It is researched clinically for muscle-wasting diseases and is used off-label in performance contexts for its potential to enhance skeletal muscle mass and recovery [3].
How it works
Follistatin binds directly to myostatin (GDF-8) and activin A extracellularly, preventing them from engaging their type I/II serine-threonine kinase receptors (ActRIIA/B) and blocking the downstream SMAD2/3 signalling cascade that restricts muscle fibre hypertrophy [4]. Releasing this "brake" disinhibits mTOR activity and activates satellite cells, driving both hypertrophy of existing fibres and hyperplasia through myoblast proliferation [4]. Because follistatin also suppresses activin-driven FSH secretion from the pituitary, its effects are not limited to muscle — it influences the hypothalamic–pituitary–gonadal (HPG) axis and reproductive biology [1][10].
Risks & side effects
Most important: Because follistatin broadly suppresses activin — which has tumour-suppressor roles in some tissues — exogenous use carries a theoretical but unresolved risk of promoting tumour growth, and serum follistatin levels are elevated across multiple cancer types [12][16]. Long-term human safety data from direct peptide injection is essentially absent, and no regulatory body has approved this compound for healthy-subject use [14].
Common
Serious
- HPG-axis dysregulation — follistatin suppresses FSH via activin antagonism, with documented FSH suppression up to ~75%, potentially disrupting reproductive function in both sexes [10][8]
- Connective-tissue lag injury — rapid muscle hypertrophy can outpace tendon and ligament adaptation, increasing risk of tears and strains [7][10]
- Theoretical tumour promotion — activin inhibition may remove tumour-suppressor signalling; serum follistatin is elevated in lung, gastric, hepatocellular, and other cancers [12][16]
- Product impurity / mislabelling risk — studies show fewer than half of commercial 'follistatin' supplements contain authentic follistatin; some contain unidentified growth-promoting peptides [8]
Rare
- Central serous chorioretinopathy (CSCR / retinal changes) — documented anecdotally in a bodybuilding cohort [10]
- Cardiac / cardiomyopathy risk — myostatin plays a role in cardiac energy homeostasis; systemic myostatin inhibition carries uncharacterised cardiac risks [14]
- Unknown long-term systemic effects — no controlled long-term human injection data exist [9][14]
Safety & harm reduction
- Active or suspected cancer — especially ovarian, prostate, or any malignancy where activin may play a tumour-suppressive role [12][14]
- Pregnancy or attempting to conceive — follistatin is integral to reproductive biology and embryonic development; contraindicated [8]
- Personal or family history of cancer without extensive oncology consultation [6]
- Cardiovascular disease or cardiomyopathy — systemic myostatin inhibition carries uncharacterised cardiac risks [14]
- Baseline and periodic FSH / LH / estradiol / testosterone — to detect HPG-axis suppression [10][8]
- Reproductive hormone panel (both sexes) before and after any cycle [10]
- Musculoskeletal check — monitor tendons and connective tissue for signs of strain given risk of muscle-tendon mismatch [7]
- Cancer screening discussion with a physician given theoretical tumour-promotion risk [12]
- Other myostatin inhibitors (e.g. YK-11): additive suppression — compounding effects and risks are unknown [3]
- Anabolic steroids / SARMs: combined HPG-axis disruption; FSH suppression may be compounded [10]
- Oncology drugs / chemotherapy: follistatin-driven activin inhibition could theoretically reduce anti-tumour efficacy [14]
- Short cycles are recommended due to FSH-suppressive and reproductive endocrine effects; long continuous use is not supported by any evidence [11]
- Cycle length in community reports ranges 10–30 days; this is not medically endorsed [13]
- Source verification is critical — fewer than half of commercial products contain authentic follistatin [8]
- Do not use outside a supervised clinical or research setting; no approved dosing protocol exists for healthy subjects [14]
Dosage context
No approved therapeutic dosing exists for direct peptide injection in healthy humans. Community-reported ranges are 100–300 mcg/day for cycles of 10–30 days (subcutaneous or intramuscular), but these figures are extrapolated from gene-therapy studies using viral-vector delivery, which have fundamentally different pharmacokinetics — they are not medically endorsed and should not be treated as safe guidelines [13][11]. Given that exogenous recombinant follistatin protein has an estimated half-life of ~1 hour [15], direct-injection community dosing is poorly characterised. Exercise extreme caution.
Sources
- 1.PMC – Inhibition of Myostatin with Emphasis on Follistatin (2009)
- 2.ScienceDirect – Follistatin complexes Myostatin and antagonises myogenesis inhibition (2004)
- 3.Swolverine – Follistatin and Myostatin Inhibition (2025)
- 4.PeptaHub – Follistatin-344 Research Guide (2026)
- 5.ScienceDirect – Discovery of a follistatin-derived myostatin inhibitory peptide (2019)
- 6.MyPeptideMatch – Follistatin 344 Side Effects (2026)
- 7.Peptides Unleashed – Follistatin 344 Overview (2026)
- 8.MediSearch – Understanding Follistatin Supplements: Benefits and Risks
- 9.Peptide Reference – Follistatin Dosage, Half-Life & Research (2026)
- 10.PeptideInsight – Follistatin-344 Research Evidence & Safety Profile (2026)
- 11.The Peptide Catalog – Follistatin-344 Dosing Guide (2026)
- 12.PMC – Serum Follistatin Levels and Lung Cancer (2018)
- 13.PeptideMania – Follistatin 344: How to Use, Benefits & Risks (2025)
- 14.Superpower – Follistatin: A Myostatin-Inhibiting Glycoprotein (2026)
- 15.USPTO Patent – Follistatin Fusion Protein FS315 Half-Life Data
- 16.SelfHacked – Follistatin Benefits and Side Effects (2026)
This information is provided for educational and harm-reduction purposes only. It is not medical advice. These substances can carry serious health risks; effects and safe use vary by individual. Consult a qualified healthcare professional before use. Legal status varies by country — it is your responsibility to know your local law. We do not encourage misuse.