How much does pharmacogenomic testing actually reduce adverse drug reactions?
The strongest evidence comes from a large, prospective European trial (the PREPARE study) that tested a pre-emptive panel of pharmacogenomic markers in routine clinical care across seven healthcare systems. It found a 30% reduction in the risk of developing clinically relevant toxicities [7]. That means for every 100 patients tested, roughly 30 fewer would experience a serious side effect compared to standard prescribing.
In a randomized trial of 665 patients with depression, those whose antidepressants were chosen based on pharmacogenomic testing had significantly fewer adverse drug reactions than those treated by clinician experience alone [1]. At 12 weeks, the testing group also had higher remission rates (31% vs. 20%) and response rates (48.7% vs. 37.3%) [1]. The authors concluded that testing 'can provide greater assistance in the treatment of depression.'
For children with complex medical conditions, a study at a pediatric hospital found that pharmacogenomic testing led to dosing recommendations that deviated from standard regimens in 80% of patients in a pre-emptive cohort and 36.8% in a point-of-care cohort [2]. This suggests that many children would otherwise receive drugs at doses that are either ineffective or unsafe.
Where does pharmacogenomic testing work best, and where does it fall short?
The most dramatic successes are for severe, life-threatening skin reactions. For example, the HLA-B*15:02 allele strongly predicts carbamazepine-induced Stevens-Johnson syndrome, and the HLA-B*58:01 allele predicts allopurinol hypersensitivity syndrome [4]. Screening for these markers before prescribing has been shown to prevent these reactions entirely in susceptible populations [4].
For psychiatric side effects, the picture is more mixed. A study of levetiracetam (an epilepsy drug) found that a polygenic risk score for schizophrenia was a risk factor for drug-induced psychosis, but no single genetic variant was strongly predictive [5]. The authors noted that larger sample sizes are needed to identify reliable genetic signals for psychiatric ADRs [5].
For gastrointestinal side effects from colchicine (a heart drug), a genome-wide study identified two genetic regions linked to a higher risk of stomach upset, but these findings need replication before they can guide prescribing [3].
Race and ethnicity also matter. One analysis showed that pharmacogenomic variants that differ in frequency between racial groups can lead to excess ADRs in minority populations if prescribing is based on frequencies from the majority White population [6]. For example, the study predicted 700 excess ADRs per 1,000 patients for a recessive-effect model in Black and Hispanic groups compared to White patients for certain chemotherapy drugs [6]. This means that ignoring genetic differences between groups can worsen health disparities.
What are the caveats and unanswered questions?
Not all pharmacogenomic tests are equally validated. The evidence is strongest for a handful of well-studied gene-drug pairs (e.g., DPYD for fluoropyrimidine chemotherapy, HLA-B*57:01 for abacavir) [7]. For many other drugs, the genetic predictors are less certain.
Cost-effectiveness is still being debated. While the PREPARE study showed feasibility and a 30% risk reduction, the authors noted that questions remain about whether pre-emptive panel testing is cost-effective in all healthcare settings [7].
Most pharmacogenomic guidelines are based on studies in people of European ancestry. The transferability of these guidelines to non-European populations is uncertain [7]. Rare genetic variants that are not detected by current genotyping panels may also be important [7].
Finally, the depression trial was not blinded (clinicians knew which patients had testing), which could bias results [1]. And the pediatric study was a single-center cohort, not a randomized trial [2].
About These Sources
This answer is built on 7 peer-reviewed studies — published from 2021 to 2024, 1 from 2024 or later, 4 in Q1 journals, collectively cited 124 times — selected as the most relevant from 7 studies that passed quality screening, drawn from 72 papers retrieved from a database of over 500 million.
Sources used in this answer
Effect of pharmacogenomic testing on the clinical treatment of patients with depressive disorder: A randomized clinical trial
In a randomized trial of 665 patients with depression, pharmacogenomic testing-guided treatment led to higher remission rates (31% vs. 20% at 12 weeks) and fewer adverse drug reactions compared to clinician-guided treatment.
Assessment of the Implementation of Pharmacogenomic Testing in a Pediatric Tertiary Care Setting
In a cohort study of 172 children at a pediatric hospital, pharmacogenomic testing led to nonstandard dosing recommendations in 80% of a pre-emptive cohort and 36.8% of a point-of-care cohort, indicating many children would otherwise receive inappropriate doses.
Pharmacogenomics of the Efficacy and Safety of Colchicine in COLCOT
In a post-hoc pharmacogenomic study of the COLCOT trial (1,522 participants), two genetic regions were associated with gastrointestinal side effects from colchicine, but no genetic variants reached significance for cardiovascular efficacy.
Pharmacogenomics of cutaneous adverse drug reactions as implication for precision medicine
This review highlights that HLA-B*15:02 and HLA-B*58:01 alleles strongly predict severe cutaneous adverse drug reactions (e.g., Stevens-Johnson syndrome) from carbamazepine and allopurinol, and screening programs have successfully prevented these reactions.
A pharmacogenomic assessment of psychiatric adverse drug reactions to levetiracetam
In a case-control study of levetiracetam users, a polygenic risk score for schizophrenia was associated with drug-induced psychotic reactions, but no single common or rare genetic variant was significantly predictive.
The Apportionment of Pharmacogenomic Variation: Race, Ethnicity, and Adverse Drug Reactions
This analysis found that 97.3% of pharmacogenomic variation falls within racial groups, but variants that differ between groups can still cause excess adverse drug reactions in minority populations (e.g., 700 excess ADRs per 1,000 patients predicted for Black and Hispanic groups for certain chemotherapy drugs).
Implementation of pre‐emptive testing of a pharmacogenomic panel in clinical practice: Where do we stand?
The PREPARE study, a large prospective randomized trial across seven European healthcare systems, showed that pre-emptive pharmacogenomic panel testing is feasible and reduces the risk of clinically relevant toxicities by 30%.