Follistatin

Key points

• Follistatin is a natural protein that binds and blocks signals in the myostatin and activin family.
• Blocking myostatin can, in animals, lead to larger muscles, which is the basis of the interest in it.
• Most of the work is laboratory and animal research, including gene therapy, not treatments you can inject.
• It is not a licensed medicine in the UK, and myostatin blockers are prohibited in sport.

Quick facts

What it is

Natural protein that blocks myostatin

Studied for

Muscle growth (mostly animal and gene therapy work)

UK status

Not a licensed medicine; sold for research use

Human evidence

Very limited; no trials of an injectable product

In sport

On the WADA Prohibited List

How it works

Myostatin is a signal that limits how much muscle the body builds. Follistatin binds myostatin and related signals, taking the brake off and allowing more muscle growth, at least in animal studies. Much of the serious research uses gene therapy to make the body produce follistatin, which is very different from injecting a peptide bought online.

What the evidence shows

The muscle effects are mainly from animal work and early gene therapy research. There are no controlled trials showing that an injected follistatin product safely builds muscle in healthy people, no settled dose, and no long term safety data. The marketing of follistatin for muscle runs well ahead of the evidence.

What it does not settle

• There are no controlled human trials of an injectable follistatin for muscle.
• Long term safety is unknown, and blocking myostatin widely could have effects beyond muscle.
• Products are not quality assessed, so purity and contents vary.

Side effects

Common

• Side effects in people are not well characterised, since proper human studies of injected follistatin are lacking.
• As with any injected product, reactions at the injection site would be expected.

Less common but serious

• Interfering broadly with the myostatin and activin system could affect tissues beyond muscle, which is not well understood.
• Because there is no licensed product, the dose, purity and contents of material bought online cannot be verified.

Report any suspected side effect through the MHRA Yellow Card scheme.

UK legal status and access

Follistatin has no UK marketing authorisation, so it is not a licensed medicine and is not offered by registered clinics or pharmacies. It is sold online labelled for research use, and gene therapy versions exist only in a research setting. A research label does not mean a product has been assessed for safety or quality.

Common questions