Two people take the same tablet at the same dose. One feels the benefit; the other notices little effect, or more side effects. Age, other medicines and health conditions all play a part, and so do genes. Pharmacogenomic testing looks at that last piece.
This guide explains what the pharmacogenomic (PGx) test in the BPR catalogue measures, how the results are meant to be used, and why the MTHFR test, which often appears next to it, deserves a more cautious reading.
What pharmacogenomic testing is
Pharmacogenomics studies how inherited differences in our genes affect the way we respond to medicines, both how well they work and how safe they are. Differences in drug response between people are common, and genes are one of the reasons. As genetic testing becomes more widely available, health systems in many countries are working out how to bring it into everyday prescribing (Pirmohamed, 2023).
Many of these genes code for enzymes, mostly in the liver, that switch medicines on or break them down. If an enzyme works faster or slower than usual, the amount of active medicine in the body can be different from what the standard dose expects.
A clear example: CYP2C19 and clopidogrel
Clopidogrel is a medicine used to reduce the stickiness of platelets. It needs to be activated by an enzyme called CYP2C19. An international guideline explains that people whose CYP2C19 gene makes them "intermediate" or "poor" metabolisers form less of the active drug, have reduced platelet inhibition and a higher risk of cardiovascular and cerebrovascular events while on clopidogrel (Lee et al., 2022).
In the UK, NICE has published guidance on CYP2C19 genotype testing to guide clopidogrel use after an ischaemic stroke or transient ischaemic attack (NICE DG59). It is one of the clearest cases where a gene result changes a prescribing decision.
What the LML pharmacogenomic test covers
According to LML, the Pharmacogenomic Test:
- uses a saliva sample collected at home with a kit;
- covers over 78 commonly prescribed medicines across areas such as mental health, pain and cardiovascular care;
- supports personalised prescribing for clopidogrel, in line with NICE guidance;
- is UKCA marked and registered with the MHRA;
- comes with a report written for you and your healthcare provider;
- has results about 30 days after the sample reaches the laboratory.
Because your genes do not change, LML describes it as a one-time test with results you can use for life. That matches the general guidance for this topic: usually done once, ideally with a professional who can explain how it fits your situation.
How to use a PGx result safely
A pharmacogenomic report is information for your prescriber, not an instruction for you. Please do not stop, start or change the dose of any medicine because of a PGx result. Take the report to your GP, pharmacist or specialist, who can weigh it alongside your other medicines, kidney and liver function, and the reason the medicine was prescribed.
It also helps to know the limits. A PGx test looks at specific genes. It does not measure how well a medicine is working for you today, and a "normal" result does not mean a medicine will suit you perfectly. Implementation in health systems is still developing, and many clinicians are still becoming familiar with these reports (Pirmohamed, 2023).
