Test Before You Treat: What the Latest Research Says About Precision Testing

Most prescriptions still begin with an educated guess. A clinician chooses the medication and dose that works for most people, then waits to see whether this patient is one of them. When it doesn’t work, or causes side effects, the cycle starts over.

A growing body of research says there is a better first step: test first, then treat.

Nearly everyone carries a gene that matters

In an analysis of 487,409 people in the UK Biobank, 99.5% carried at least one genetic variant that may cause an atypical response to a medication, on average affecting more than 10 drugs. Nearly a quarter had already been prescribed a drug they were predicted to respond to atypically.⁵ The FDA now maintains a public table of gene-drug associations where it believes the evidence is strong enough to matter for prescribing.⁶

In other words, genetic differences in drug response aren’t rare exceptions. They are the norm.

30% fewer adverse drug reactions

The strongest evidence comes from PREPARE, published in The Lancet in 2023. Researchers enrolled 6,944 patients across 18 hospitals, nine community health centers and 28 community pharmacies in seven European countries. Half received prescriptions guided by a 12-gene panel; half received standard care.

Patients whose prescriptions were guided by genetic testing had 30% fewer clinically relevant adverse drug reactions (21.5% vs. 28.6%).¹

Better results in depression

Depression is one of the clearest examples of trial-and-error prescribing. In the PRIME Care randomized trial of 1,944 veterans at 22 VA medical centers, published in JAMA, clinicians with pharmacogenomic results chose antidepressants with no predicted drug-gene interaction 59.3% of the time, compared with 25.7% in usual care.²

A 2025 follow-up analysis found a 27% higher rate of remission and a 21% higher rate of response in the testing group, with the benefit holding steady over six months.³

Lower total cost of care

Precision testing also makes financial sense. A December 2025 study of 1,042 Medicare Advantage patients in a community primary care setting found that 44% were taking three or more medications affected by known genetic variants. Compared with matched patients who weren’t tested, the tested group showed a trend toward $1,827 in net savings per patient per year.⁴

The same principle, beyond prescriptions

The research above is about medications. But the principle behind it, that individuals differ and testing reveals how, is shaping wellness and longevity care too.

In the NOW randomized controlled trial, adults in a weight-management program who received gene-based nutrition guidance made larger and longer-lasting improvements in their diet than those who received standard advice.⁷ The evidence for gene-based nutrition is earlier than for pharmacogenomics, but the direction is consistent: personalized information changes behavior and outcomes.

For practices that offer supplements, peptides or biologics, starting with assessment is simply good medicine. It gives clinicians a baseline, helps match the right option to the right patient, and sets honest expectations from the start.

What this means for your practice

• Fewer surprises: fewer adverse reactions and fewer medication changes.
• Faster results: patients reach effective treatment sooner, especially in depression.
• A clear differentiator: patients increasingly expect care built around them.
• A one-time test with lasting value: genetic results stay relevant for future prescriptions.

For more background, see our earlier piece, Why Pharmacogenomics Is Becoming Standard of Care.

Sources

1. Swen JJ, et al. A 12-gene pharmacogenetic panel to prevent adverse drug reactions (PREPARE). The Lancet. 2023;401:347–356. www.thelancet.com
2. Oslin DW, et al. Effect of pharmacogenomic testing for drug-gene interactions on medication selection and remission of symptoms in major depressive disorder (PRIME Care). JAMA. 2022;328(2):151–161. pubmed.ncbi.nlm.nih.gov
3. Persistent benefit of pharmacogenomic testing on initial remission and response rates in patients with major depressive disorder. Frontiers in Pharmacology. 2025. www.frontiersin.org
4. Multi-gene pharmacogenomic testing in a community-based setting is feasible and reduces total healthcare costs. Clinical and Translational Science. 2025;18(12):e70418. pubmed.ncbi.nlm.nih.gov
5. McInnes G, et al. Pharmacogenetics at scale: an analysis of the UK Biobank. Clinical Pharmacology & Therapeutics. 2021. pmc.ncbi.nlm.nih.gov
6. U.S. Food and Drug Administration. Table of Pharmacogenetic Associations. www.fda.gov
7. Horne J, et al. Enhanced long-term dietary change and adherence in a nutrigenomics-guided lifestyle intervention (NOW randomised controlled trial). BMJ Nutrition, Prevention & Health. 2020;3(1):49–59. pmc.ncbi.nlm.nih.gov

Disclosure: The Dacey Group works with precision testing partners and may be compensated when practices adopt their programs, including as an authorized master distributor for Genesis Regenerative. This article is for informational purposes for healthcare professionals and is not medical advice. Study results describe the populations studied and may not apply to every patient.

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