Pharmacodynamics is best described as:

Pharmacodynamics is best described as what the drug does to the body. This branch of pharmacology focuses on the biochemical and physiological effects of drugs and their mechanisms of action. It encompasses how drugs interact with cellular receptors, the subsequent effects these interactions generate, and the overall impact on bodily functions. Understanding pharmacodynamics is crucial for paramedics, as it provides insight into how specific medications alter patient conditions, guide treatment protocols, and inform the decision-making process regarding medication administration.

For context, the choice that describes what the body does to the drug refers to pharmacokinetics, which involves absorption, distribution, metabolism, and excretion of medications. The study of a drug's chemical properties is also not strictly related to pharmacodynamics but rather to pharmaceutical chemistry or pharmacognosy. Lastly, while the effects of drug administration on patients are important, they are more a concern of clinical pharmacology, which encompasses both pharmacodynamics and pharmacokinetics.