Follistatin: myostatin inhibition, and the distance between gene therapy and a vial
The myostatin story is real biology with striking animal results and a genuine clinical programme behind it. What is sold as follistatin is not what that programme delivered, and the difference is not a technicality — it changes what can be expected and what is known about risk.
Regulatory status. Research compound — no FDA approval. Gene therapy versions in clinical trials for muscular dystrophy. Extreme caution warranted. That is the app’s own field, reproduced here rather than summarised. It means no regulator has reviewed a manufacturer’s evidence for identity, purity, potency or safety in people for this compound, so nothing below is a marketing claim about a product you can buy.
Purity, identity and concentration are therefore unverified by anyone but whoever made the vial. The storage rule in the fact box below is general practice for this formulation rather than a specification for a particular product: General handling practice for this formulation. Your supplier’s own insert or COA overrides anything here.
This page names no vendor, no clinic and no testing service, and there is no discount code anywhere on this site — the moment a page like this recommends where to buy, it stops being information.
- Also known as
- FS-344, FST-344, myostatin inhibitor
- Class
- Myostatin pathway
- Regulatory status
- Research compound — no FDA approval. Gene therapy versions in clinical trials for muscular dystrophy. Extreme caution warranted.
- Before mixing
- Sealed powder tolerates room temperature in transit, but keep it refrigerated at 2–8 °C (36–46 °F) for anything beyond a few weeks, or frozen for months. Keep it dark — the carton it shipped in is doing a job.
- After mixing
- Once reconstituted with bacteriostatic water: refrigerate at 2–8 °C and use within about 28 days. The benzyl alcohol in bacteriostatic water is what buys that window — plain sterile water has no preservative, so a vial mixed with it should be treated as one sitting only. Kits are usually ten vials: only the one you mixed is on that 28-day clock — the sealed ones keep their own, much longer shelf life, so store them as powder, not as solution.
- What ruins it
- Do not freeze a reconstituted vial. Repeated freeze–thaw is one of the more reliable ways to degrade a peptide.
- Handling caveat
- General handling practice for this formulation. Your supplier’s own insert or COA overrides anything here.
The brake, and what removing it does
Established clinical use Myostatin, also called GDF-8, is a member of the TGF-β family that limits skeletal muscle growth. Animals and the small number of people with loss-of- function mutations in the myostatin gene have substantially more muscle mass than expected. Follistatin is an endogenous glycoprotein that binds myostatin and activin and neutralises them, which removes that brake. All of that is settled biology.
Because it works through a pathway entirely separate from the androgen receptor, it does not carry the mechanism behind the androgenic effects or the suppression of the hypothalamic-pituitary-testicular axis that testosterone does. That is a real mechanistic distinction and it is often presented as though it also implies a better safety profile. It does not. It means the risks are different ones, and less well characterised.
Off-label or community practice The clinical work has been almost entirely gene therapy: a viral vector delivering the follistatin gene to muscle, studied in Becker and inclusion body myositis in small early-phase trials. Those studies reported functional changes in some participants and are the strongest human evidence the molecule has. They also delivered sustained local expression inside muscle tissue — a fundamentally different exposure from an injected peptide.
Why the injected version is a different question
Animal-only or theoretical Follistatin is a glycoprotein, not a small peptide, and circulating follistatin is cleared quickly. Whether a subcutaneous injection produces meaningful myostatin neutralisation in muscle, at what exposure, and for how long, has not been established in humans. The app records a research protocol of 100mcg daily in short runs with breaks; that figure comes from community practice rather than from a trial, and this page presents it as the app’s entry rather than as a recommendation.
The pharmaceutical industry has also tested this pathway directly, with monoclonal antibodies and receptor decoys against myostatin and activin in muscular dystrophy, sarcopenia and cachexia. Several increased lean mass. Most failed to improve function, and the programmes were largely discontinued. That is the most instructive result in the whole field: the pathway does what it is supposed to do to muscle size, and size did not translate into people doing more.
Product identity is a further problem specific to this compound. Recombinant glycoproteins are difficult and expensive to manufacture correctly, glycosylation affects activity, and there is no way for a buyer to confirm any of it. This site names no vendor.
Risks worth taking seriously
Animal-only or theoretical The concern the app records first is the right one. Myostatin and activin signalling participates in growth restraint in tissues beyond muscle, and activin signalling has tumour-suppressive roles in several cell types. Whether systemic inhibition affects cancer risk in humans is unknown, and unknown here means untested rather than reassuring. Anyone with a personal or family history of malignancy should treat that as a conversation with an oncologist rather than a footnote.
The antibody trials also surfaced effects that had not been predicted from the muscle story, including reports of gynaecomastia and epistaxis attributed to off-target activity within the TGF-β family. A pathway this central rarely turns out to have a single consequence.
Monitoring, per the app, is body composition, liver enzymes, a complete blood count and general cancer screening awareness. Note what that list cannot do: none of those tests detects the theoretical risk this compound carries. They are the reasonable general panel, not a safety net, and the appropriate step before any of it is a discussion with a doctor who knows your history.
The dosing rows the app records
Off-label or community practice Reproduced from the app’s reference so you can see what it holds, not as a recommendation. Which row applies to a particular person, if any, is a clinical decision this page does not make — and rows describing supraphysiological or post-cycle use are filtered out before this table is built, so what you see here is a subset.
| Label | Amount | Route and frequency | Duration recorded |
|---|---|---|---|
| Research protocol | 100mcg/day | SubQ daily | 2-4 week cycles with breaks |
What the app monitors alongside it
The panel below is the app’s own monitoring note for Follistatin, verbatim. None of the analytes it names has a page here yet.
- Monitoring panel
- Body composition tracking, liver enzymes, general cancer screening awareness, CBC.
Drawbacks and risks the app records
From the app’s own entry. The cancer item is not a disclaimer added for form — it is the reason the pharmaceutical programmes were watched as closely as they were.
- Very limited human peptide injection data
- Expensive and difficult to source with verified purity
- Long-term safety completely unknown
- Cancer risk concern — myostatin inhibition could affect tumor suppression
- Optimal dosing not established
- Mechanisms complex — systemic effects uncertain
Questions people actually ask
Is follistatin approved for anything?
No. Gene therapy approaches have been studied in small early-phase muscular dystrophy trials. There is no approved follistatin product and no approved myostatin inhibitor for muscle growth.
Do the gene therapy results apply to an injection?
Not directly. Those trials delivered a gene to muscle tissue for sustained local expression. An injected glycoprotein that clears from circulation quickly is a different exposure, and it has not been studied the same way.
Why did the pharmaceutical myostatin programmes stop?
Several increased lean mass without improving function in the populations studied, which is not enough to approve a drug. The pathway worked; the outcome did not follow.
What about the cancer concern?
Activin and myostatin signalling has growth-restraining roles outside muscle, so systemic inhibition raises a theoretical question that no human study has answered. It is worth raising with a doctor, particularly with any personal or family cancer history.
Where the load-bearing numbers come from
Named rather than linked. Publisher URLs move, and a citation that resolves to a 404 two years from now is worse than one you can search for by name — every entry below is findable from the title and year alone.
- Myostatin limits skeletal muscle growth
- Established; supported by loss-of-function phenotypes in animals and humans
- Follistatin binds and neutralises myostatin and activin
- Established biochemistry
- Gene therapy trials in muscular dystrophy
- Small early-phase studies reporting functional change; the strongest human data
- Injected peptide protocols
- Community practice; app.html records 100mcg daily in short runs, with no trial behind it
- Lean mass without functional benefit
- Repeated finding across discontinued myostatin and activin antibody programmes
- Cancer risk from systemic inhibition
- Theoretical, from tumour-suppressive roles of activin signalling; untested in humans
A compound with no validated marker needs an unusually careful record of everything else. TherapyLog keeps the dose, the measurements and the notes together.
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