Pharmacodynamics is the study of the biochemical and physiologic effects of drugs. The effects can include those manifested within animals, microorganisms or combinations of organisms. Pharmacodynamics and pharmacokinetics are the main branches of pharmacology being itself a topic of biology interested in the study of the interactions between both endogenous and exogenous chemical substances with living organisms. In particular pharmacodynamics is the study of how a drug affects an organism, whereas pharmacokinetics is the study of how the organism affects the drug. Both together influence dosing, benefit and adverse effects.