Whether a product is regulated as a medicine in the UK depends partly on how it is presented, not only on what it contains. Most research peptides hold no marketing authorisation and are not medicines in law.
The published literature on BPC-157 is overwhelmingly preclinical rodent work, much of it from a single research group. It holds no medicines approval anywhere and has been on the WADA Prohibited List since 2022.
Solid-phase peptide synthesis anchors the growing chain to a resin and adds amino acids one at a time. Small losses compound at every cycle, which is why longer sequences give lower yields and messier impurity profiles.
A peptide is a chain of amino acids joined by peptide bonds. The boundary between peptide, polypeptide and protein is convention rather than chemistry — and chain length shapes stability, synthesis and analysis.