Follistatin 315

Key points

• Follistatin 315 is the main circulating form of follistatin, which binds and blocks myostatin.
• Blocking myostatin can, in animals, allow more muscle growth.
• Most of the research is laboratory and animal work, including gene therapy, not an injectable people can rely on.
• It has no UK marketing authorisation, and myostatin blockers are prohibited in sport.

Quick facts

What it is

Circulating form of follistatin (blocks myostatin)

Studied for

Muscle growth (mostly animal and gene therapy)

UK status

Not a licensed medicine; sold for research use

In sport

On the WADA Prohibited List

How it works

Myostatin limits how much muscle the body builds. Follistatin binds it and takes the brake off. The 315 form circulates more freely in the blood, compared with the 344 form, which binds more to cell surfaces. In animals this can increase muscle, but there is no good human evidence for an injected product.

What the evidence shows

The muscle effects are mainly from animal and gene therapy research. There are no controlled trials showing an injected follistatin safely builds muscle in people, and no settled dose.

What it does not settle

• There are no controlled human trials of an injectable follistatin.
• Long term safety is unknown, and blocking myostatin widely could affect tissues beyond muscle.
• Products are not quality assessed.

Side effects

Less common but serious

• Interfering broadly with the myostatin 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 315 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.

Common questions