Pharmacogenomic Testing
Pharmacogenomics looks at how your genes affect the way your body handles some medicines. For a handful of medicines it can prevent serious side effects. For most, it adds little. Here’s how to tell the difference.
Your genes can’t tell you which antidepressant you’ll love. They can tell you which ones your liver might mishandle.
How it works
- Liver enzymes such as CYP2D6 and CYP2C19 break down many medicines. Gene differences make some people slow or very fast at this.
- Slow: the medicine builds up and side effects are more likely.
- Fast: the medicine may not work, or, for some, turns into too much of its active form.
- A different set of genes (HLA) can flag a risk of rare, severe allergic reactions.
Where it really matters
- Azathioprine and mercaptopurine: a TPMT test before starting. About 1 in 300 people have very low TPMT and can get dangerous blood problems. Covered by Medicare.
- Abacavir (HIV): an HLA-B*57:01 test before starting prevents a serious reaction. Covered by Medicare.
- Carbamazepine and allopurinol: HLA tests can flag a risk of severe skin reactions, which is more common in some Asian backgrounds. Not on Medicare.
- Codeine: ultra-rapid CYP2D6 metabolisers can make too much morphine.
- Clopidogrel: CYP2C19 poor metabolisers may get less protection after a heart stent.
Commercial panels
- You can buy panels covering dozens of medicines, sometimes through pharmacies, for a few hundred dollars.
- Reports can be vague ("poor metaboliser") and many skip the HLA genes linked to the most serious reactions.
- For antidepressants, a panel may help choose a dose or avoid a medicine, but it can’t predict which one will work for you.
- Results don’t change, so keep a copy and share it with every doctor and pharmacist.
Treatments lacking evidence
- Using a panel to choose an ADHD medicine, a diet or supplements: there’s no good evidence it helps.
- Changing or stopping a medicine on a test result alone, without your doctor.
Talk to your GP if
- You’re about to start azathioprine, mercaptopurine, abacavir, carbamazepine or allopurinol
- You’ve had unusual side effects at normal doses, or several medicines haven’t worked
- You have a commercial test report and want it checked
Common questions
What is pharmacogenomic testing?
A DNA test, usually a cheek swab or blood test, that looks at genes affecting how your body processes some medicines.
Is pharmacogenomic testing covered by Medicare?
Only for a few medicines, such as TPMT testing before azathioprine and HLA-B*57:01 before abacavir. Broader panels are paid privately.
Can a DNA test tell me which antidepressant will work?
Not reliably. It can flag medicines you may break down too fast or too slowly, which helps with dosing, but it can’t predict which one will work best for you.
Do I need to repeat the test?
No. Your genes don’t change, so keep the report and share it with your doctors and pharmacist.
Helpful resources
Evidence and more information
maladywise.com/pharmacogenomics/