Answer : 3. "Pharmacology"
Explanation :

It is concerned with the sources, chemical properties, and effects of the drugs.

It is a branch of medicine, biology, and pharmaceutical sciences concerned with drug or medication action, where a drug may be defined as any artificial, natural, or endogenous molecule which exerts a biochemical or physiological effect on the cell, tissue, organ, or organism.

To understand this we need to consider what a drug is, how it affects our physical, emotional, and psychological well-being, the type of drug being used, the modes of administration, how the drug is absorbed, and the characteristics of the person taking the drug.