The first-pass effect is a pharmacological phenomenon in which a medication undergoes metabolism at a specific location in the body. The first-pass effect decreases the active drug's concentration upon reaching systemic circulation or its site of action. The first-pass effect is often associated with the liver, a major site of drug metabolism. However, the first-pass effect can also occur in the body's lungs, vasculature, gastrointestinal tract, and other metabolically active tissues. This ef...
