Understanding pharmacogenomics would not be possible without sequencing the genomes of many people and comparing them, and then comparing their response to medicines. But we have also learned that a person's genome sequence is not everything when it comes to medication responses. The human body is a very complicated machine, and the instructions written in our DNA are just part of the process.

There are some cases, as with the breast cancer treatment tamoxifen, where a small study showed that there might be a relationship between someone's response to the medicine and a variant in theCYP2D6gene. However, this finding did not appear to be true in a larger study that involved many more people. That's why at this time, the U.S. Food and Drug Administration (FDA) labeling for tamoxifen does not recommendCYP2D6pharmacogenomic testing, butthe issue is still being reviewedas more research is conducted.

Another gene in the sameCYPfamily, calledCYP2C19, has variations which affect how your body can useclopidogrel(more commonly known as Plavix). This medication is a "blood thinner" which helps prevent blood clots, and thus reduces your risk of strokes or some heart attacks. If yourCYP2C19protein is not working properly due to a mutation in the gene, then you will not be able toprocess clopidogrel, and you need either a different dose or a different medication. As it turns out, these variants inCYP2C19are also more common in those with Asian ancestry. Although testing for variants in this gene is also not routinely recommended, you may wish to speak with your healthcare provider about the test if you are given a prescription for clopidogrel, particularly if you have East Asian family members.

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Pharmacogenomics - Genome.gov