Understanding Pharmacogenomics: Why Medications Affect People Differently

Have you ever wondered why a medication that works perfectly for your friend does nothing for you? Or why you experience side effects that others don't? The answer often lies in your genes.

Pharmacogenomics is the study of how genetic variation affects drug response. It's one of the most immediately practical applications of genetic testing.

How your genes process medications

When you take a medication, your body needs to absorb it, distribute it, metabolize it, and eventually eliminate it. Each step involves enzymes — proteins coded by your genes. Different genetic variants produce enzymes with different activity levels.

If you're a "rapid metabolizer" for a particular drug, you break it down quickly. Standard doses might not work well because the medication clears your system too fast. If you're a "poor metabolizer," the drug stays in your system longer, potentially leading to side effects or toxicity at normal doses.

The CYP450 family

The cytochrome P450 enzymes are responsible for metabolizing about 70-80% of all medications. Genes like CYP2D6, CYP2C19, and CYP3A4 have well-documented variants that affect how you process everything from antidepressants to pain medications to heart drugs.

For example, about 7% of Caucasians are poor metabolizers for CYP2D6. For them, codeine — which needs to be converted to morphine by CYP2D6 to work — provides little pain relief. On the other hand, ultra-rapid metabolizers convert codeine too quickly, potentially causing dangerous opioid effects.

Beyond metabolism: sensitivity and response

Genes also affect how sensitive you are to medications once they reach their targets. Variants in receptor genes can make you more or less responsive to certain drugs. This is why finding the right antidepressant, for example, often involves trial and error — different people's brains literally respond differently to the same compounds.

The bottom line

Pharmacogenomic testing can help you and your healthcare providers make smarter decisions about medications — choosing the right drugs and doses based on your biology rather than population averages. It's not about replacing medical judgment; it's about informing it with better data.