Fig. (4) Genetic polymorphism affecting individual drug responses. The study dealing with how much drug is required to exert an optimal effect, is known as pharmacokinetics, while pharmacodynamics deals with the relationship between the concentration of the drug at the receptor and the pharmacological response because of it. Any variations in the genetic sequence, also known as Single Nucleotide Polymorphisms (SNPs) can affect the overall response of the drug. It can cause the drug to metabolize at an exponential rate or slow it down altogether. This can cause either a no response or overdose, both of which are not optimal effects.