The subgroup of all those individuals whose DNA causes their bodies to respond in a specific way to a given drug or synthetic food ingredient, is known as a HAPLOTYPE. For example, one haplotype (subgroup) of pediatric leukemia patients suffers severe & life-threatening reactions to some commonly-used leukemia treatment drugs, due to the variation (i.e., SNP) in the thiopurine S-methyl transferase gene (allele) in their genome.

Another example is the 2010 discovery by John Bartlett that a SNP known as CEP17, found on chromosome 17 in the DNA of one haplotype of women, is a "highly significant indicator" that breast cancer tumors in those women will respond to the class of chemotherapy drugs known as anthracyclines (i.e., anti-tumor antibiotics which interfere with enzymes involved in DNA replication).

Another example is that consumption of the tyrosine kinase inhibitor drug gefinitib (Iressa) works to control tumors of non-small-cell lung cancer in people who possess a mutation (i.e., the SNP which codes-for the epidermal growth factor receptor) within their lung cancer tumors.

Another example is that consumption of the pharmaceuticals tolbutamide, warfarin, or phenytoin can be riskier for people who possess a mutation (i.e., an SNP which codes-for less or no expression of CYP2C9) within their liver tissue. That is because the CYP269 enzyme causes rapid metabolism of tolbutamide, warfarin, phenytoin (and some other pharmaceuticals); so the "typical dose" could result in higher-than-expected bloodstream levels of those pharmaceuticals in people possessing that particular SNP.

Another example is that consumption of sodium-containing food ingredients tends to cause dangerous increase in blood pressure (hypertension) among the African-American people living in the United States, more often than among other ethnic groups living in the United States.