What if there were a test based on your genes that could tell you what medications to avoid or which ones your doctor should prescribe rather than others for you? This test exists and is called pharmacogenomic testing and using the results can help you and your doctor fine-tune the medications you use.
Pharmacogenomics (also called pharmacogenetics) is the study of how different genes affect how well medications work. A person’s genes affect every aspect of their health, so it is no surprise that genes affect how an individual responds to medications. We all have that friend who can drink coffee at all hours and still sleeps like a baby, and the one who has one cup of tea after noon and can’t get to sleep that night. The different way they respond lies in their genes, which are why different people respond differently to different drugs.
These differences may also explain why some people have a serious side effect with a medication or why a medication that gets results for most people just doesn’t work for them. Putting it another way, a dose that works safely for most people is an overdose in some and is too low for others. Pharmacogenomics is uncovering the reasons behind these variations.
Different people have slightly different versions of the same gene and these different versions may behave differently. Many genes control how medications (or drugs like caffeine and opioids) are metabolized– broken down into other chemicals–in the body. Medications are metabolized primarily in the liver, and a genetic difference can make one person’s liver metabolize the drug faster or slower, or not at all. People for whom a drug works well are called responders and those for whom a drug doesn’t work or works weakly are called nonresponders.
According to the National Institute of General Medical Sciences, part of the National Institutes of Health, one of the genes that makes a big difference in drug metabolism is one that creates a liver enzyme called CYP2D6. This enzyme is used in the metabolism of about one in every four prescription medications. There are dozens of different versions of the CYP2D6 gene, most of which don’t make a difference one way or the other. People usually get two copies of the gene, but some people get more than two copies, which means that they metabolize certain drugs better leading to a stronger action of the drug. Others have fewer CYP2D6 genes or copies that don’t work well, which means that they need larger doses of some drugs or that those drugs will not work for them at all.
There are more than 200 drugs for which genetic differences are known to change how a person metabolizes them. The Food and Drug Administration now requires pharmacogenomic information on the labeling insert for about 200 prescription medications. Many of the drugs for which genetics makes a difference are involved in the treatment of cancer, in treating mental health problems like depression and attention deficit disorder, or in anesthesia.
Pharmacogenomic testing is done just like most other DNA testing. DNA is obtained by swabbing the inside of the cheek or by obtaining a saliva sample in a small tube. Some pharmacogenomic testing companies prefer to use a blood sample. The sample is sent away and results come back in a few weeks.
The cost for the testing is usually between $250 and $500. However, health insurance won’t always pay for pharmacogenomic testing. If the test is ordered by a physician to see why certain treatments are not working, an insurance company is more likely to pay for it. But many people are willing to pay for pharmacogenomic testing out of their own pocket because they believe this information is useful.
Several companies do pharmacogenomic testing and more genetic research is being conducted in this area. More genes that cause variations in how medications affect the body are being discovered every day. However, many of the tests offered are limited in the number of genes they look at.
If you are interested in having a pharmacogenomic test done, talk to your doctor.
One good thing: Once you’ve had a pharmacogenomic test done, you generally don’t have to do it again. Your genes don’t change so the results stay the same. However, you may need to be tested again in the future as research uncovers more genetic variations that affect medication use.