What field of study does pharmacology encompass?

Pharmacology is defined as the study of drug sources, chemistry, and effects on biological systems. This encompasses a broad range of topics including how drugs interact with the body, their therapeutic effects, side effects, and mechanisms of action. A comprehensive understanding of pharmacology is critical for healthcare professionals because it informs how medications can be used to treat various conditions safely and effectively.

In contrast, other fields of study mentioned in the other choices focus on different aspects of medicine. The study of poisons and their effects refers to toxicology, which is a specific subset of pharmacology but does not encompass the broader range of drug studies. Medical histories and practices pertain more to medical history or health records rather than pharmacological science. Patient care and nursing practices are essential components of healthcare but are distinct from the pharmacological principles that underlie drug utilization and effects.

Thus, the option specifying the study of drug sources, chemistry, and actions aptly encapsulates the essence of pharmacology as a discipline and highlights its importance in the medical field.