Individual genetic variations are suspected to be the most influential factor with respect to drug efficacy, specifically, single nucleotide polymorphisms (SNP) in genes responsible for the transportation and metabolism of a particular drug. Correlations have been discovered between the genotype of the various SNPs located within the drug-metabolising enzymes and the overall efficacy of a particular drug. This information could then potentially be used to prescribe personalised medication based on an individual's genetic profile.