No highly selective agonists or antagonists for the M5 receptor have been discovered as of 2018, but several non-selective muscarinic agonists and antagonists have significant affinity for M5.
The lack of selective M5 receptor ligands is one of the main reasons that the medical community has such a limited understanding of the M5 receptors effects as the possibility that any and/or all effects of non-selective ligands may be due to interactions with other receptors can not be ruled out. Some data may be obtained by observing which effects are common among semi-selective ligands (ex. a ligand of M1 and M5, a ligand of M2 and M5, and a ligand of M3 and M5), but until both a selective agonist and a selective antagonist of the M5 receptor are developed this data must be considered merely theoretical.
^Grant MK, El-Fakahany EE (October 2005). “Persistent binding and functional antagonism by xanomeline at the muscarinic M5 receptor”. J. Pharmacol. Exp. Ther. 315 (1): 313–9. doi:10.1124/jpet.105.090134. PMID16002459.
Crespo P, Xu N, Daniotti JL, et al. (1994). “Signaling through transforming G protein-coupled receptors in NIH 3T3 cells involves c-Raf activation. Evidence for a protein kinase C-independent pathway”. J. Biol. Chem. 269 (33): 21103–9. PMID8063729.
Haga K, Kameyama K, Haga T, et al. (1996). “Phosphorylation of human m1 muscarinic acetylcholine receptors by G protein-coupled receptor kinase 2 and protein kinase C.”. J. Biol. Chem. 271 (5): 2776–82. doi:10.1074/jbc.271.5.2776. PMID8576254.
Kohn EC, Alessandro R, Probst J, et al. (1996). “Identification and molecular characterization of a m5 muscarinic receptor in A2058 human melanoma cells. Coupling to inhibition of adenylyl cyclase and stimulation of phospholipase A2”. J. Biol. Chem. 271 (29): 17476–84. doi:10.1074/jbc.271.29.17476. PMID8663391.
Burstein ES, Spalding TA, Brann MR (1998). “The second intracellular loop of the m5 muscarinic receptor is the switch which enables G-protein coupling”. J. Biol. Chem. 273 (38): 24322–7. doi:10.1074/jbc.273.38.24322. PMID9733718.
Sato KZ, Fujii T, Watanabe Y, et al. (1999). “Diversity of mRNA expression for muscarinic acetylcholine receptor subtypes and neuronal nicotinic acetylcholine receptor subunits in human mononuclear leukocytes and leukemic cell lines”. Neurosci. Lett. 266 (1): 17–20. doi:10.1016/S0304-3940(99)00259-1. PMID10336173.
Wang H, Han H, Zhang L, et al. (2001). “Expression of multiple subtypes of muscarinic receptors and cellular distribution in the human heart”. Mol. Pharmacol. 59 (5): 1029–36. PMID11306684.
Buchli R, Ndoye A, Arredondo J, et al. (2002). “Identification and characterization of muscarinic acetylcholine receptor subtypes expressed in human skin melanocytes”. Mol. Cell. Biochem. 228 (1–2): 57–72. doi:10.1023/A:1013368509855. PMID11855742.
Fujii T, Watanabe Y, Inoue T, Kawashima K (2003). “Upregulation of mRNA encoding the M5 muscarinic acetylcholine receptor in human T- and B-lymphocytes during immunological responses”. Neurochem. Res. 28 (3–4): 423–9. doi:10.1023/A:1022840416292. PMID12675126.
Ota T, Suzuki Y, Nishikawa T, et al. (2004). “Complete sequencing and characterization of 21,243 full-length human cDNAs”. Nat. Genet. 36 (1): 40–5. doi:10.1038/ng1285. PMID14702039.
De Luca V, Wang H, Squassina A, et al. (2004). “Linkage of M5 muscarinic and alpha7-nicotinic receptor genes on 15q13 to schizophrenia”. Neuropsychobiology. 50 (2): 124–7. doi:10.1159/000079102. PMID15292665.
Qu J, Zhou X, Xie R, et al. (2006). “The presence of m1 to m5 receptors in human sclera: evidence of the sclera as a potential site of action for muscarinic receptor antagonists”. Curr. Eye Res. 31 (7–8): 587–97. doi:10.1080/02713680600770609. PMID16877267.