6,7-dihydroxy Bergamottin (6,7-DHB) is a potent inhibitor of CYP3A4 (IC50 = 25 µM). It appears to be the primary compound in grapefruit juice that is responsible for inhibition of testosterone 6β-hydrolase activity. Ingestion of grapefruit juice during treatment regimes with drugs normally metabolized by cytochrome P450 enzymes of the CYP3A subfamily results in a substantial increase in plasma concentration of these agents. However, giving a patient grapefruit juice or just 6,7-DHB could be advantageous in cases where a drug is metabolized too quickly by CYP3A4.