Which process is directly involved in how the body handles ingested drugs?

The body handles ingested drugs primarily through the process of metabolism. Metabolism refers to the biochemical processes that occur within the body to convert substances, such as drugs, into more manageable forms. This process usually takes place in the liver, where enzymes break down drugs into metabolites. These metabolites can either be active, contributing to the drug's effects, or inactive, allowing for their eventual excretion from the body.

Metabolism is crucial for the detoxification and elimination of drugs, as it helps to reduce their potency and prepare them for excretion through urine or bile. Understanding how different drugs undergo metabolic processes is essential for determining dosage, efficacy, and the potential for toxicity or adverse effects.

Other processes listed, such as excretion, respiration, and circulation, play important roles in the overall pharmacokinetics of drugs but are not directly involved in the transformation of substances. Excretion relates to the removal of drug metabolites from the body, respiration pertains to gas exchange in the lungs, and circulation involves the transport of blood and substances throughout the body. Thus, while all these processes are interconnected in handling substances in the body, metabolism specifically deals with the chemical transformation of drugs after they are ingested.