FAAH encodes fatty acid amide hydrolase an enzyme that degrades anandamide and other biological molecules. Anandamide, is an endogenous cannabinoid agonist.
Knockout mice without FAAH show reduced pain sensation and elevated anandamide. [PMID 15362158]
A fairly common FAAH gene SNP, rs324420, significantly reduces the activity of the FAAH enzyme. Studies have reported that the rs324420(A;A) genotype is generally associated with insensitivity to pain, and more specifically is associated with a reduced need for postoperative analgesia, increased postoperative nausea and vomiting induced by opioids, and decreased anxiety-linked behaviours.[PMID 30929760]
In 2019, a woman was described with extreme insensitivity to pain, presumably due to co-inheriting a single rs324420(A) allele plus an 8kb microdeletion downstream of the FAAH gene that in some way appears to disrupt the function of a nearby transcribed FAAH pseudogene.[PMID 30929760]