Is Peptide YY legal in the United Kingdom?

A gut hormone released after meals alongside GLP-1. Infused into 12 lean and 12 obese people it cut buffet intake by about 30 percent in both, but the rodent finding it was built on failed a published multi-laboratory replication, and nausea kept it from becoming a drug.

Peptide YY is a 36 amino acid hormone released from the same intestinal L cells that release GLP-1 and oxyntomodulin, in proportion to the calories in a meal. The enzyme DPP-4 clips two residues off the front to make PYY3-36, which prefers the Y2 receptor, a presynaptic inhibitory receptor on the appetite-driving NPY neurons of the hypothalamus.

Mechanism: Established in humans by infusion: PYY3-36 at postprandial concentrations reduces appetite ratings and ad libitum energy intake for hours, lowers plasma ghrelin, and does so equally in lean and obese people. Established in rodents but contested (see the dispute): peripheral PYY3-36 reduces food intake through the Y2 receptor, an effect absent in Y2 receptor knockout mice, with increased c-Fos in the arcuate nucleus, reduced hypothalamic NPY mRNA and inhibition of NPY neuron firing that disinhibits adjacent POMC neurons.

Regulatory history: Not FDA-approved. No PYY or PYY3-36 product is approved anywhere; native PYY3-36 has been studied in people only by intravenous or subcutaneous infusion.

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 Peptide YY 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.