PubMed, ScienceDirect, and Google Scholar databases were searched using the following keywords in various combinations: endocannabinoid system, endocannabinoids, interstitial cystitis, bladder pain syndrome, cannabinoid receptors, fatty acid amide hydrolase, monoacylglycerol lipase, anandamide, 2-arachidonoylglycerol, and biomarker. The gene discussed is FAAH; the disease is interstitial cystitis.