The pharmacology field focuses on drug interactions on biological systems. It also explores the biological effects, chemical properties, and the sources of therapeutic drugs and their uses. Topics within the field vary substantially - learning about pharmacology requires you to be knowledgeable about cell biology, pharmacodynamics, drug action, and how the body responds to drugs.
Majoring in pharmacology will expose you to the mechanics of drugs and the design and testing phases of new medications. The clinical side of the major will allow you to study about drug dosage and the various ways by which you can minimize risks while improving treatments.
A pharmacology major will allow you to jump right into the field, or pursue further education in medical or graduate school.
With the amount of knowledge at your disposal and a little bit of determination, you could perhaps one day revolutionize the way we practice medicine and invent a drug that could cure cancer or AIDS.