Medicines That Heal but Can Harm: Pharmacogenetics (PGx)
At a glance
Ever wondered why a medicine can be a lifesaver for someone else but a disaster for you? Pharmacogenetics (PGx) explains why, and why it should be a priority.
- Big problem: A noticeable chunk of hospital beds is filled by people harmed by their medicines.
- Different genes, different reactions: The same dose can be too weak, just right, or dangerously strong depending on your genes.
- Small panel, big reach: A few dozen key genes already influence how we respond to 100+ common medicines.
- Future-proof info: One PGx test can guide many prescriptions across your lifetime, not just one drug today.
Medicine heals and hurts
Recent national and international studies suggest that around 2–6% of all hospital admissions are primarily caused by adverse drug reactions (ADRs); in older adults and those on many medicines, the proportion is even higher. (1) (2)
Among emergency readmissions, about 1 in 5 can be traced back to unwanted side effects, and many of these are considered potentially preventable. (3) (4)
At the same time, 1.4 billion adults worldwide are living with hypertension (high blood pressure) , a major reason for taking long-term medication. Nearly half don’t know they have it, and only about 1 in 5 have their blood pressure under good control. (5) (6)
So we have a double challenge:
- Many people need complex medication plans.
- A significant number get hurt by them or don’t respond as expected.
Pharmacogenetics is one of the tools that can help shift that balance.
What is pharmacogenetics, really?
Pharmacogenetics (PGx) looks at how your genes influence the way you process and respond to medicines:
- Enzyme genes affect how quickly you break down a drug.
- Transporter genes affect where the drug goes in the body.
- Receptor and target genes affect how strongly it works.
The Clinical Pharmacogenetics Implementation Consortium (CPIC) publishes evidence-based guidelines designed to help clinicians understand HOW available genetic test results should be used to optimize drug therapy (rather than WHETHER tests should be ordered). (7)
As summarized in recent CPIC publications, CPIC guidelines cover 34 genes and 164 drugs. turning genetic results into concrete prescribing advice. (8)
In practice, a relatively small panel of genes can touch a large fraction of common prescriptions over a person’s life, because many widely used drug classes (pain, mental health, heart/clotting, cholesterol, oncology, immunology) have well-described gene–drug interactions. (9) (10)
3.Concrete gene–drug examples (that people actually recognise)
Here are some everyday medicines people recognise where small genetic differences can change how well the drug works or how likely side effects are.
| Health area | Gene(s) | Medicines people recognise | What the gene can change |
|---|---|---|---|
| Pain & anaesthesia | CYP2D6 | Codeine Tramadol | Low CYP2D6 activity: little or no activation, so you may get no pain relief. Very high CYP2D6 activity: rapid activation, so you may make too much morphine and have a higher risk of breathing problems. |
| Mental health | CYP2C19 | Citalopram Escitalopram Sertraline | Slow metabolisers: higher blood levels, so more side-effects. Ultra-rapid metabolisers: lower blood levels, so less benefit. |
| Mental health | CYP2D6 | Tricyclic antidepressants (e.g., amitriptyline, nortriptyline) Many antipsychotics | Low CYP2D6 activity: higher drug exposure, which can increase sedation and other side-effects; for some tricyclics, it can increase the risk of rhythm problems. Very high CYP2D6 activity: lower drug exposure, which can reduce benefit for some drugs. |
| Heart & clotting | CYP2C9 + VKORC1 | Warfarin | Certain variants increase sensitivity, so a much lower dose is needed. Without dose adjustment, the risk of serious bleeding is higher, especially early in treatment. |
| Heart & clotting | CYP2C19 | Clopidogrel | Loss-of-function variants reduce activation, so clopidogrel may work less well. This can increase risk in high-risk settings, for example after stent placement. |
| Cholesterol & statins | SLCO1B1 | Simvastatin (and some other statins) | Risk variants raise statin levels in muscle, which can increase muscle pain. Rarely, this can progress to serious muscle injury. |
| Cancer | DPYD | 5-fluorouracil (5-FU) Capecitabine | Reduced DPYD activity means the drug clears more slowly. Standard doses can cause severe or life-threatening toxicity. |
| Autoimmune / IBD / transplant | TPMT + NUDT15 | Azathioprine 6-mercaptopurine | Low activity can cause metabolite build-up. This can lead to dangerous bone-marrow suppression (low white cells and higher infection risk). |
| Severe skin reactions | HLA-B*57:01 | Abacavir | Strongly predicts a dangerous hypersensitivity syndrome. |
| Severe skin reactions | HLA-B*15:02 | Carbamazepine (especially in some Asian ancestries) | Associated with Stevens�Johnson syndrome and toxic epidermal necrolysis. Risk is higher in populations where the variant is more common. |
Note: These are not rare edge cases. Older adults on multiple medicines are particularly exposed to harm from drug interactions and dose sensitivity. For evidence-based, implementation-focused actionability, see CPIC and FDA resources (7) (10) .
What pharmacogenetics can and can’t do
- It can turn trial and error into smarter first guesses, especially for drugs where CPIC provides actionable dosing/selection guidance. (7)(8)
- It won’t magically pick the one perfect drug, because response also depends on diagnosis accuracy, dose, kidney/liver function, interactions, adherence, and time.
- It does help reduce preventable harm for specific drug–gene pairs by flagging higher-risk situations (e.g., toxicity risk or non-response risk) before dose escalation. (10)(9)
- It doesn’t replace diagnosis, clinical monitoring, or listening to symptoms , it improves the decision-making around drug choice and dose when used in context.
How HealthCode.Gene fits in
At HealthCode.Gene, we fit into pharmacogenetics in two ways: we model, and we make it usable — always anchored to evidence-based guidance (CPIC/FDA) and the patient’s phenotype and medication context. (7) (10)
- Model: Build evidence-weighted models that integrate PGx signals with phenotype (age, kidney/liver function, comedications, dose history, symptoms) to support safer dose stratification and adverse reaction risk profiling.
- Translate: Turn lab reports and model outputs into clear, plain-language “what this means / what to do next” explainers for patients, clinicians, and product teams.
- Enable use: Create visuals/one-pagers and support research groups, clinics/medical spas, and startups in designing and communicating PGx-aware services and pilots, with guardrails that prevent over-interpretation.
References
- Beeler PE, et al. Hospitalisations Related to Adverse Drug Reactions in Switzerland in 2012–2019: Characteristics, In-Hospital Mortality and Spontaneous Reporting Rate . Drugs . 2023. https://link.springer.com/article/10.1007/s40264-023-01319-y
- Pirmohamed M, James S, Meakin S, et al. Adverse drug reactions as cause of admission to hospital: prospective analysis of 18,820 patients . BMJ . 2004;329(7456):15–19. doi:10.1136/bmj.329.7456.15. https://pubmed.ncbi.nlm.nih.gov/15231615/
- Davies EC, Green CF, Taylor S, Williamson PR, Mottram DR, Pirmohamed M. Emergency re-admissions to hospital due to adverse drug reactions within 1 year of the index admission . British Journal of Clinical Pharmacology . 2010. https://pubmed.ncbi.nlm.nih.gov/21039769/
- Banholzer S, Jäger J, Christen S, et al. Retrospective analysis of adverse drug reactions leading to short-term emergency hospital readmission . Swiss Medical Weekly . 2021. https://smw.ch/index.php/smw/article/view/2945
- World Health Organization (WHO). Hypertension (Fact sheet). https://www.who.int/news-room/fact-sheets/detail/hypertension
- World Health Organization (WHO). Uncontrolled high blood pressure puts over a billion people at risk . News release (23 Sep 2025). https://www.who.int/news/item/23-09-2025-uncontrolled-high-blood-pressure-puts-over-a-billion-people-at-risk
- Clinical Pharmacogenetics Implementation Consortium (CPIC). CPIC Guidelines (evidence-based recommendations for how to use available PGx results). https://cpicpgx.org/guidelines/
- Caudle KE, Whirl-Carrillo M, Relling MV, et al. Advancing Clinical Pharmacogenomics Worldwide Through the Clinical Pharmacogenetics Implementation Consortium (CPIC) . Clinical Pharmacology & Therapeutics . 2025;118(6):1512–1522. doi:10.1002/cpt.70005. https://pubmed.ncbi.nlm.nih.gov/40678821/
- Clinical Pharmacogenetics Implementation Consortium (CPIC). Genes–Drugs . https://cpicpgx.org/genes-drugs/
- U.S. Food and Drug Administration (FDA). Table of Pharmacogenomic Biomarkers in Drug Labeling . https://www.fda.gov/drugs/science-and-research-drugs/table-pharmacogenomic-biomarkers-drug-labeling
Downloadable Resources
why genes matter for health
get PDFDownload our PDF guide “Why Genes Matter for Health” for a handy summary of key references on polygenic risk scores, pharmacogenetics, and gene–lifestyle interactions, designed to inform health decisions and enhance patient outcomes.
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