Endomorphin

Tetrapeptide endogenous opioids (Tyr-Pro-Trp-Phe-NH₂ and Tyr-Pro-Phe-Phe-NH₂) with the highest known affinity and selectivity for μ-opioid receptors among natural opioid peptides. Studied for pain modulation with potentially reduced side effects compared to morphine due to their selectivity.