No More ‘One Size Fits All’

For most of modern medicine's history, prescribing has worked on averages. A drug is trialled across a population, an average effective dose is established, and that dose becomes the starting point for everyone. It works well much of the time — but it leaves a substantial minority of people either under-treated, over-treated, or dealing with side effects that were, in principle, predictable.

Personalised medicine aims to replace that average with something closer to the individual.

What are biomarkers?

Personalising drug therapy works by identifying measurable biological characteristics — biomarkers — that predict how a person will respond to a specific medicine. A biomarker might be a genetic variant, a protein level, or a metabolic measurement.

In some cases the presence of a particular biomarker signals a poor response to a whole class of drug, which should influence the initial choice rather than being discovered after months of failed treatment.

A worked example: clopidogrel

Clopidogrel is a widely prescribed antiplatelet drug, given to millions of people to reduce the risk of clots after heart attacks, stents and strokes. It is a prodrug, meaning the body must convert it into its active form before it does anything useful. That conversion depends on an enzyme produced by the CYP2C19 gene.

People carrying reduced-function variants of that gene convert less of the drug, get a weaker antiplatelet effect, and remain at elevated risk of a further event — while taking their medication exactly as prescribed. Testing before prescribing allows an alternative antiplatelet to be chosen from the outset.

The genetic basis of metabolism

Genetics also strongly influences how quickly medicines are broken down, and therefore what dose a person actually needs.

Warfarin is the classic illustration. It is highly effective at preventing clots, but the dose required varies dramatically between individuals — by more than tenfold — largely due to variation in the CYP2C9 and VKORC1 genes. Because warfarin's therapeutic window is narrow, getting this wrong means either no protection or a serious bleeding risk. The conventional approach has been careful dose titration with regular INR blood monitoring; genotype-guided dosing offers a way to start closer to the right dose in the first place.

It is worth noting that DOACs such as apixaban and rivaroxaban have now displaced warfarin for many UK patients, precisely because they avoid this variability. Warfarin remains necessary for certain groups, including people with mechanical heart valves.

Why it runs in families

The genes governing drug response are inherited, which means a result relevant to you is often relevant to your blood relatives too. A finding about how you metabolise a common medicine may prove useful to a sibling, parent or child years later.

Beyond genetics

Personalised medicine is broader than genotype. Kidney and liver function, age, weight, other prescribed medicines, over-the-counter products, smoking, alcohol and diet all shape how a drug behaves — frequently more than genetics does. Good personalised prescribing accounts for all of it.

Realistic expectations

Pharmacogenomics is a genuinely promising field, and the NHS is expanding its use, but it is applied selectively rather than universally. The evidence is robust for some drug–gene pairs and thin for others. A genetic result is one input into a clinical decision, not the decision itself.

Never stop, start or adjust a prescribed medicine on the basis of a genetic result alone. Speak to the clinician who prescribes it.

Testing with Rightangled

Rightangled's DNA tests assess genetic markers relevant to health risk and medication response. Results are reviewed by our clinical team, which includes GPhC-registered independent prescribers, with medical oversight from our doctor, Dr Abdullah, so you receive practical context rather than raw data.

Verify us with the General Pharmaceutical Council (registration 9011933), see our LegitScript certification, and read reviews on Trustpilot.

This article is for general information and does not replace personalised medical advice. Never change prescribed medication without speaking to your clinician.