How does omeprazole affect the metabolism and effects of diazepam?

Omeprazole inhibits diazepam’s CYP2C19 metabolism, prolonging its elimination half-life and increasing its AUC by approximately 30–120% in CYP2C19 extensive metabolisers but not slow metabolisers with low diazepam clearance, thereby increasing diazepam’s action; a diazepam dose reduction may be necessary.