What is Pharmacogenomics?

Pharmacogenomics is the study of how your genetics change your response to medicine.

Are you a clinician? Visit our Pharmacogenomics for Clinicians(opens in new window) page.

Check the PharmGKB Glossary(opens in new window) for definitions of common genetic and pharmacogenetic terms.

Genetics 101

How does genetic variation affect how I respond to a medicine?

How can I get my pharmacogenomic information?

Pharmacogenomics in action

Navigate to...

Genetics 101

You can think of your DNA as a code made up of the letters A, C, G and T. These four letters can be used to spell out many different instructions, known as genes(opens in new window).

Genes tell your cells how to make proteins(opens in new window), the building blocks of the body. When there is a change in how a gene is "spelled", the resulting protein may be made differently. This can change how it works and can affect how you respond to medication.

Each individual person will have different spelling changes in their DNA, which is why we see genetic variation(opens in new window) between people.

Humans have over 20,000 genes, coding for proteins that play different roles in the body. Every person has two copies of each gene, one inherited or passed down from each parent. Because each of your parents has different spelling changes in their DNA, the two copies are different from each other. These different versions of the same gene are known as alleles.

Genetic variation is what makes us different from one another, such as the differences in our height and eye color. Most genetic variation doesn't affect our health, but sometimes changes can happen in important genes and lead to consequences such as diseases or an altered response to medication.

Changes to your DNA can be small, like single nucleotide polymorphisms (SNPs)(opens in new window), where a single letter is changed to a different letter. Or they can be a lot bigger where many DNA letters are added, deleted or rearranged. Scientists use rsID numbers(opens in new window) to identify different types of DNA changes and where they are in the genome.

For example, rs4149056(opens in new window) identifies where the letter C has replaced the letter T at a certain position in the gene known as SLCO1B1. This change affects how well the protein coded for by this gene works. In this case, individuals who have the letter C have an increased risk of developing muscle disease when they are treated with the drug simvastatin(opens in new window).

In genetics, it is important to know what is going on in both alleles, so genetic information is often reported as a genotype(opens in new window), which describes the gene spellings found on both copies of your genes. For example, if you wanted to find out your genotype at rs4149056(opens in new window), a genetic test would look at whether you had a "C" or a "T" on each of your two SLCO1B1 copies. Your test results could be "CT", meaning you had one SLCO1B1 copy with the letter C and one copy with the letter T. The results could also be "CC", if both your SLCO1B1 copies had the letter C, or "TT" if both copies had the letter T.

Sometimes, the function of a gene is not affected unless there are multiple changes all present within the gene. Instead of describing each one of these changes, scientists can group them all together and give this group a specific name or number – this group is called a haplotype(opens in new window). For example, the *17 haplotype in the gene CYP2C19 consists of four changes at different positions in the gene. When describing the haplotype state of both gene copies, the term diplotype(opens in new window) is used instead of genotype.