Pharmacodynamics is the study of the biochemical and physiologic effects of the medicine (especially pharmaceutical drugs). The effects can include those manifested within animals (including humans), microorganisms, or combinations of organisms (for example, infection). Pharmacodynamics and pharmacokinetics are the most branches of pharmacology, being itself a subject of biology curious about 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 that the study of how the organism affects the drug. Both together influence dosing, benefit, and adverse effects. Pharmacodynamics is usually abbreviated as PD and pharmacokinetics as PK, especially in combined reference.