What is the first step that a drug undergoes after administration?

After a drug is administered, the first step it undergoes is absorption into the bloodstream. This process involves the drug moving from the site of administration into the circulatory system, where it can be transported to its target sites in the body. Absorption is influenced by various factors, including the drug's formulation, route of administration (such as oral, intravenous, or topical), and the physiological conditions of the individual (like gastric pH or blood flow to the absorption site).

Once in the bloodstream, the drug can then bind to plasma proteins, be distributed to different tissues, metabolized, and eventually excreted from the body. Understanding the absorption process is crucial, as it affects the onset, intensity, and duration of the drug's therapeutic effect and is a foundational concept in pharmacology.