“Pharmaco-Whaat?! Understanding pharmacogenomic testing and how it could aid your doctor in prescribing medication

Pharmacogenomics is an area of genetics focused on understanding how our unique genetic code determines how we might respond to certain medications.

I asked a group of genetic counselors who specialize in this area to write up their top tips for understanding pharmacogenomic testing, a term you might see shortened to “PGx”.

It’s a timely and relevant topic to post about because :

1) 23andMe got FDA approval near the end of 2018 to start releasing some reports directly to consumers.

2) Doctors and other clinicians are starting to order the more comprehensive type of PGx testing in the clinical setting at an increasing rate.

Don’t take any of what you read here as personal medical advice, though! Make sure to consult your doctor before making any changes to the medications you use or the dosage you take.


“Pharmaco-Whaat?! Understanding pharmacogenomic testing and how it could aid your doctor in prescribing medication”

A Guest Post written by these members of the National Society of Genetic Counselors with expertise in Pharmacogenomics: Jennifer Eichmeyer, Emily Glogowski, Rachel Mills, and Tara Schmidlen

Many of us take medications to stay healthy and treat conditions such as depression and cardiovascular disease. However, some people respond differently to some medicines, and part of that difference is due to our genetic makeup. Genetic tests that identify and characterize these variations are available, and you may be wondering if those tests are a good idea for you. Here are some points to consider:

1.     The term “pharmacogenetics” technically refers to one gene, and the term “pharmacogenomics” technically refers to multiple genes. However, the terms are used interchangeably.

2.     Current medical practice often uses a trial and error approach to prescribing medications. The initial choice and dose of medications are often based on population data, but individuals vary significantly in the way they respond.  Only about 50-75% of individuals taking a medication will have the intended response (Spear et al., 2001).

3.     Pharmacogenomic testing analyzes specific genetic variants to better understand how a person may respond to medications (Weinshilboum et al., 2017). These variants can be associated with the way the body uses or breaks down the medication (Van Driest et al., 2014).  The goals of pharmacogenomic testing are to shorten the trial-and-error period, optimize medication dose, and reduce the risk of side effects.

4.     Genetics are not the only factor that influence a person’s response to medications. They are just one piece of the puzzle. Medication responses can be affected by gender, age, race, other medications, other medical conditions, and diet. There may still be a trial and error period when starting a new medication, but one goal of pharmacogenomic testing is to shorten it.

5.      Pharmacogenomic testing can be helpful in many situations, like these:

·       Pain control using medications like codeine and opioids

·       Psychiatric disorders using medications like antidepressants

·       Cardiovascular disease using medications like statins and anticoagulants

·       Gastrointestinal conditions using medications like proton pump inhibitors

·       Neurological conditions using medications like anti-epileptics

·       Cancer and chemotherapy

·       Other medicines like anti-diabetics or general anesthesia

However, not all medications in these categories have enough data to support changing prescribing guidelines. So, it is important to speak to an informed medical provider, about which medications will have the most benefit from pharmacogenomic testing.

6.     Pharmacogenomic testing can be done anytime. Some people test prior to taking a medication, and others test after because may not be responding to treatment or have had side effects (Relling et al., 2011; Dunnenberger et al., 2015). Healthy people might consider testing so the pharmacogenomics information would be available if they need a new medication in the future. This would avoid waiting for results when the medication is prescribed.

7.     Evidence-based dosing guidelines are freely available. Guidelines can help doctors use pharmacogenomic test results to prescribe medications (Relling et al., 2011; Whirl-Carrillo et al., 2012; Swen et al., 2008; 2011; FDA 2017). These guidelines are updated frequently. They can be accessed online at www.cpicpgx.org and www.pharmgkb.org

8.     Pharmacogenomic information is included in the Food and Drug Administration (FDA) drug labels for over 100 medications.  Some FDA labels provide specific actions that can be taken based on genetic information. You can see a table of genetic information found in drug labels at www.fda.gov/drugs/scienceresearch/researchareas/pharmacogenetics/ucm083378.htm.

9.     Each lab test has its own unique list of medication-genes covered by their test. If you are interested on a particular medication, make sure the lab and test includes it.  Some labs offer smaller, disease-specific panels. Others offer broader panels with many diseases, genes, and medicines. 

10.  If you have pharmacogenomics testing, share the results with your healthcare providers. Your genetic results do not change overtime. So this information could be useful for future prescriptions. A genetic counselor can help you sort through the different choices so you can have the test that is most useful and important to you.

You may have heard that the FDA authorized the testing company, 23andMe, to report on 33 genetic variants that may be associated with medication metabolism. However, the FDA also included some precautions. In particularly, the FDA recommended that 23andMe’s test should not be used to determine medication use.

If you plan to use pharmacogenomic information for medical care, it may be better to start with a test ordered by a healthcare provider. Any pharmacogenomic testing conducted by 23andMe will require confirmatory testing in a clinical grade lab.  If you order 23andMe for other recreational reasons, you can still pay attention to the pharmacogenomics results, but seek out an informed medical provider to address your questions. If confirmed by a clinical grade laboratory, those results could be useful for your future care.


Dunnenberger et al. (2015) Annu. Rev. Pharmacol. Toxicol. 55: 89-106 (PMID: 25292429)

Relling et al. (2011) Clin. Pharmacol. Ther. 89 (3):464-7 (PMID: 21270786)

Spear et al. (2001) Trends Mol Med 7 (5):201-4 (PMID: 11325631)

Van Driest et al. (2014) Clin. Pharmacol. Ther. 95 (4):423-31 (PMID: 24253661)

Verbelen et al. (2017) Pharmacogenomics J. 17(5):395-402 (PMID: 28607506)

Weinshilboum et al. (2017) Mayo Clin. Proc. 92 (11):1711-1722 (PMID: 29101939)

Whirl-Carrillo et al. (2012) Clin PharmacolTher 92(4): 41-417 (PMID: 22992668)

Swen et al. (2008) Clin. Pharmacol. Ther. 83 (5):781-7 (PMID: 18253145)

Swen et al. (2011) Clin. Pharmacol. Ther. 89 (5):662-73 (PMID: 21412232)

Table of pharmacogenomic biomarkers in drug labeling. US Food and Drug Administration. https://www.fda.gov/drugs/scienceresearch/researchareas/pharmacogenetics/ucm083378.htm. Accessed November 2017.

About the authors: Jennifer Eichmeyer, MS, LCGC has been a clinical genetic counselor for 16 years with a focus on oncology and pharmacogenetics. She is the program director for the Boise State Master of Science in Genetic Counseling Program and sees patients in her private practice. Emily Glogowski, MS, MSc, LCGC, is a genetic counselor who worked with patients in New York City for over 15 years.  She now works as a genomics consultant, educating counselors and physicians, for GeneDx.  Rachel Mills, MS, CGC is a research genetic counselor at Duke in the Center for Applied Genomics and Precision Medicine, where her research work focuses on implementation of precision medicine, particularly pharmacogenetics. Rachel is also provides tele-genetic counseling services for patients who have undergone genetic testing, including pharmacogenetic testing.  Tara Schmidlen, MS, LGC is a research genetic counselor working for Geisinger with 12 years of experience in providing telephone-based genetic counseling for adult onset complex disease and pharmacogenomics, research biobanking, and precision health research.