Pharmacodynamics is the study of the biochemical and physiological effects of drugs and the mechanisms of drug action and the relationship between drug concentration and effect.
Pharmacodynamics is the study of what a drug does to the body, as opposed to pharmacokinetics, which is the study of what a body does to a drug.
A good source for further information and posting to experts can be found courtesy of Dr. David W. A. Bourne, OU College of Pharmacy [1].
By Manan Mehta