Bilaid C is a tetrapeptide μ-opioid receptor agonist (Ki= 210 nM in HEK293 cell membranes expressing the human receptor) that has been found inPenicillium.1It inhibits forskolin-induced cAMP accumulation by 77% in HEK293 cells expressing the human μ-opioid receptor when used at a concentration of 10 μM. Bilaid C induces inward rectifying potassium channel (Kir) currents in rat locus coeruleus slices that endogenously express high levels of the μ-opioid receptor (EC50= 4.2 μM). 1.Dekan, Z., Sianati, S., Yousuf, A., et al.A tetrapeptide class of biased analgesics from an Australian fungus targets the μ-opioid receptorProc. Natl. Acad. Sci. USA116(44)22353-22358(2019)