The CYP450 enzymes in the liver may metabolize some of the drug before it extends the systemic circulation. This is known as the first-pass effect or first-pass metabolism, and it can greatly reduce the amount of the drug that reaches the bloodstream (McDonnell, PharmD, BCOP & Dang, PharmD, BCPS, 2013). As a result, the drug’s bioavailability can be diminished. Some drugs can induce CYP450 enzymes such as grapefruit juice leader to higher levels of certain medications.