Plain-English guide to how your genes can affect how medicines work for you — and when testing might be useful in Australia.
Some people respond to a medicine straight away. Others feel nothing. And a few get bad side effects at a normal dose. Part of that difference comes down to your genes — the instructions your body uses to build and run itself. Pharmacogenomics is a name for the study of how those genes affect the way your body handles medicines.
Lots of things affect how a medicine works in you — your age, your kidneys and liver, other medicines you take, what you eat, how much you weigh. Genes are one more piece. Your genes contain the recipes for the enzymes and other proteins that break down, activate, or are affected by a medicine.
If your version of a gene makes an enzyme work faster than average, some medicines might get cleared out too quickly to work. If your enzyme works slower, the medicine might build up and cause more side effects at a normal dose. For a handful of medicines, we know which genes matter and we have practical guidance on what to do about it.
This is a general information tool — not medical advice. Tick anything that applies to you and see what the guideline suggests. Your GP is the right person to decide whether testing is appropriate.
Australia's Royal Australian College of General Practitioners (RACGP) genomics guideline lists a small number of medicines where genetic variation is well established. This is not a complete list — it's the group with the strongest evidence for everyday use.
| Medicine | What it's used for | Why genes matter |
|---|---|---|
| Codeine | Pain relief | Some people don't convert codeine into its active form, so it doesn't help their pain. Others convert it too fast — a risk for side effects, especially in children and breastfeeding. |
| Some antidepressants (paroxetine, fluvoxamine) | Depression / anxiety | Some people need a lower dose because they clear the medicine slowly. Others may not respond because they clear it too quickly. |
| Clopidogrel | Blood thinner after stents or stroke | Clopidogrel needs to be activated by an enzyme. Some people activate it poorly — a different blood thinner may work better for them. |
| Warfarin | Blood thinner | Two genes affect the right starting dose. In practice, INR blood tests still guide dose in Australia — but genes explain some of the variation. |
| Simvastatin | Cholesterol | A gene variant can raise the risk of muscle pain from simvastatin. A lower dose or a different statin may be considered. |
| Abacavir | HIV treatment | People with a specific gene marker (HLA-B*57:01) can have a serious allergic reaction to abacavir. Testing is required before starting — and covered by Medicare. |
| Azathioprine / mercaptopurine (thiopurines) | Immune conditions, some cancers | People whose bodies can't break down these medicines properly can develop dangerous drops in blood counts. Testing the TPMT gene beforehand is covered by Medicare. |
Source: RACGP Genomics in general practice — Pharmacogenomics (Table 1, last revised December 2023). This is a general list — it does not tell you what to do about your own medicines. Talk to your GP.
Most pharmacogenomic tests use a saliva sample from a swab, or a small blood sample. It's not painful.
Results typically take 5–10 working days per RACGP. For urgent treatment decisions, this may be too slow.
The lab sends your GP a report describing your genetic type for each gene tested, and what it may mean for common medicines.
Your genes don't change. A pharmacogenomic result from years ago is still valid today — you don't need to repeat it.
Beyond these two, wider "panel" tests (checking many genes at once) are available privately from several Australian labs. Prices are typically a few hundred dollars. There is currently no Medicare rebate for these panels. Some private health insurance policies may partially reimburse — check with your fund before testing.
Online DNA testing kits are marketed for ancestry, "wellness", or drug response. Their pharmacogenomic sections often use the same genes discussed here, but the quality and clinical usefulness varies widely. If you've had a direct-to-consumer test:
Sources: Centre for Genetics Education (NSW Health); RACGP guideline.
Since 2019, the Australian life insurance industry has had a moratorium (voluntary cap) on the use of genetic test results in life insurance applications up to certain policy amounts. The rules are set by the Financial Services Council. Before doing any genetic test, it's worth reading the current position, because policies and thresholds change.
Sources: Centre for Genetics Education; Financial Services Council Standard No. 11.
For the two Medicare-covered tests (HLA-B*57:01 before abacavir, TPMT before thiopurines), tests are usually ordered by the specialist who is prescribing the medicine, sometimes in partnership with your GP.
For wider commercial panels, some labs accept a request from a GP directly; others require a specialist request. Your GP can advise.
No. Genes are only part of the picture. Regular medication reviews with your GP — or a formal Home Medicines Review with a pharmacist — remain the main way to keep your medicines safe, especially if you take several. Pharmacogenomics can add information for a small number of decisions, but it doesn't replace this ongoing review.
If you've had a bad reaction to a medicine, or a medicine hasn't worked when it should have — tell your GP. They can decide whether pharmacogenomic testing might help, or whether other factors (dose, timing, interactions with other medicines) are more likely to explain what you're experiencing.
This page is for information only. It is not medical advice, and does not replace advice from your doctor about your specific situation.