The first pass effect is a phenomenon in which a drug gets metabolized at a specific location in the body that results in a reduced concentration of the active drug upon reaching its site of action or the systemic circulation. The first pass effect is often associated with the liver, as this is a major site of drug metabolism. However, the first pass effect can also occur in the lungs, vasculature, gastrointestinal tract, and other metabolically active tissues in the body. This effect can become augmented by various factors such as plasma protein concentrations, enzymatic activity, and gastrointestinal motility. The extent to which a patient may experience the first pass effect varies from patient to patient, and this must also be taken into consideration when determining appropriate dosing. If the first-pass effect is exceptionally prominent in a patient, the drug may require administration via a different route to bypass the first-pass effect.