Is FGF21 legal in the United Kingdom?

A liver hormone released by fasting, sugar and protein restriction that signals through beta-klotho. Engineered analogues improved liver fibrosis in phase 2b MASH trials of 222 and 128 people; lifespan extension exists only in transgenic mice.

FGF21 is an endocrine fibroblast growth factor made mainly by the liver in response to fasting, ketogenic states, protein restriction, sugar intake and PPAR-alpha activation. Unlike the paracrine FGFs it lacks the heparin-binding domain that keeps them local, so it circulates, and it can act only on tissues that express its obligate co-receptor beta-klotho, principally fat, liver and parts of the brain.

Mechanism: Established in mice: fasting induces hepatic FGF21 through PPAR-alpha; FGF21 induces PGC-1alpha, drives fatty acid oxidation and ketogenesis, improves insulin sensitivity, suppresses growth hormone action, and causes bone loss. FGF21 signals through FGFR1c (and FGFR3c) only in the presence of beta-klotho, which is what restricts its action to fat, liver and specific brain regions.

Regulatory history: Not FDA-approved. Native FGF21 is not a drug. No FGF21 analogue (efruxifermin, pegozafermin, efimosfermin) had a Drugs@FDA record on 11 September 2026; efruxifermin and pegozafermin are in phase 3.

Licenses medicines for the UK market. A compound without a marketing authorisation is an unlicensed medicine, which can only lawfully be supplied for human use through a prescriber under the specials scheme, not sold as a research product.

The classification above is the The Longevity Archive reading of Medicines and Healthcare products Regulatory Agency listings for FGF21 at the reviewed date, not a legal opinion. Rules change, and importing, prescribing and possessing a compound can each be treated differently. Check the regulator directly before acting on anything here.