Podcast episode 138 (in German)
Follistatin and myostatin inhibitors – muscle without training, twenty years later
November 15, 2026
A boy in Berlin whose muscle brake was switched off on both gene copies showed that the idea works. After that, 3 drugs failed in 3 different ways — until a fourth attempt hit a primary endpoint for the first time, small, but on function.
What it is about
Myostatin is the body’s own brake on muscle growth, follistatin a protein that intercepts it: you do not step on the gas, you take your foot off the brake. That this works in humans was shown by a child in whom both copies of the myostatin gene were altered. The episode goes through the drugs that were supposed to come out of this, which failed once on safety, once on efficacy and once because more mass does not mean more function. The fourth attempt, apitegromab in spinal muscular atrophy, was the first to reach a primary endpoint. Added to this is what is sold as follistatin online and in Honduras, and what people report about it. What remains: so far, only strength training with enough protein has been shown to increase mass and function together.
Key points
- At age 4.5, the boy’s thigh muscle cross-section was 7.2 standard deviations above that of children his age, and he held 2 dumbbells of 3 kilos each with outstretched arms, with normal development.
- The first attempt, a decoy receptor in boys with Duchenne muscular dystrophy, was halted in April 2011 because of nosebleeds, gum bleeding and dilated skin blood vessels, all of which resolved; by 2013 it had been discontinued.
- In 2018, an antibody against myostatin missed the endpoint in 121 boys aged 6 to 15, the time to climb 4 stairs after 1 year; the study explicitly did not end for safety reasons.
- With the antibody bimagrumab in inclusion body myositis, the 6-minute walking distance of 251 people after 52 weeks did not differ from placebo in any dose group.
- Yet bimagrumab demonstrably builds muscle: in 180 people over 70 with muscle wasting, lean mass rose by 7 percent compared with 1 percent under placebo, with no difference in walking, standing up or balance.
- In the SAPPHIRE trial with 188 participants aged 2 to 21, apitegromab improved motor function in the 2- to 12-year-olds by 1.8 points, confidence interval 0.3 to 3.3.
- A laboratory bought 14 products offered online: 2 contained no matching protein at all, the other 12 a related molecule instead of the substance used in the studies.
Where the data stop
No study has given a healthy person a myostatin inhibitor and then measured strength over a relevant period. The large, clean trials ran in serious diseases; reading them as evidence for a vial from the internet mixes up 3 different things with the same name. Even the hit in spinal muscular atrophy is small, and the higher dose level on its own missed significance. For the US, an approval decision had been announced for the end of September 2026, which was still pending at the time of recording; the European application was withdrawn in September 2026.
A follistatin gene therapy in a special economic zone in Honduras costs a reported 25,000 dollars; there are no published study data. A well-known user reported a 160 percent increase in his follistatin level and more of a feeling of added substance; a rising blood level shows that something has arrived, not that it works. That expectation and social media reinforce each other here happens to anyone who tries something and listens to themselves. A gene therapy is meant to stay; there is no off switch.
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Published on November 15, 2026.
The topic in the database
- “Releasing the muscle brake”: follistatin and related substances block myostatin – the body’s own limiter of muscle growth. In humans, so far…Follistatin / myostatin inhibitors
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Information only, not medical advice and not a usage or dosage recommendation. Prescription-only and unapproved substances belong in the hands of a physician. Last updated: 2026-09-23.