Frakefamide is a tetrapeptide with an amide function at the C-terminus. The amino acid sequence of frakefamide is L-tyrosyl-D-alanyl-p-fluoro-L-phenylalanyl-Lphenylalaninamide. Hence, it contains both natural and unnatural R-amino acids. Frakefamide has shown interesting properties for use in acute and chronic pain treatment. It acts as a selective agonist on mu-opioid receptors and belongs to the dermorphin peptide family. It has been shown to be a potent peripherally acting analgesic in rats and humans. However, frakefamide had been found to have "unexpected results" in Phase II trials and AstraZeneca offered to hand the drug back.