A large randomized trial found that genotype-guided prescribing of selective serotonin reuptake inhibitors (SSRIs) for depression did not improve symptoms after three months, compared with usual care. However, among participants whose genetic profiles suggested a different medication or dose, remission at six months was higher in the genotype-guided group (48%) than in the usual-care group (39%). The study was published in JAMA Network Open.
Depression is a prevalent mental health condition characterised by persistent low mood and loss of interest, with rising rates across adults, adolescents, and younger people. The disorder’s treatment largely relies on SSRIs, which can take several weeks to show effect and may cause side effects that lead some patients to stop taking them.
Genetic differences in liver enzymes such as CYP2D6 and CYP2C19 influence how SSRIs are processed in the body. Variants in these genes can categorise people as poor, intermediate, normal, rapid, or ultrarapid metabolisers, altering drug levels. Genotype-guided prescribing uses test results to tailor the choice of drug or its dose accordingly.
The Clinical Pharmacogenetics Implementation Consortium has issued guidelines for adjusting SSRI prescriptions based on these genes, but routine genetic testing has not been widely endorsed in practice due to limited evidence. Previous trials faced criticisms related to proprietary algorithms, small samples, or not achieving primary goals.
In this new trial, researchers led by Kathryn V. Blake of Nemours Children’s Health conducted a large randomised study to test whether genotype-guided SSRI prescribing improves outcomes in routine care. The study focused on CYP2D6 and CYP2C19 and used publicly available guidelines rather than a commercial algorithm to generate recommendations.
Participants totalled 1,460 people with depression treated at nine U.S. health systems between 2021 and 2024. Participants were aged eight years or older and were about to start or adjust SSRI treatment. The cohort included 1,239 adults with an average age of 41, and 221 children and adolescents with an average age of 15; 75% were female.
Participants were randomised to either a genotype-guided group or usual care. All supplied DNA samples for analysis of CYP2D6 and CYP2C19, but only the genotype-guided group received genetic results during the trial; the usual-care group’s results were analysed after the study ended.
For those in the genotype-guided group, clinicians received recommendations about which SSRI to prescribe and at what dose, delivered via electronic health record alerts, consult notes, or pharmacist input, with consideration of other medications that can slow CYP2D6 activity. The SSRIs included were sertraline, escitalopram, citalopram, fluvoxamine, and paroxetine. Clinicians were not obliged to follow these recommendations.
The most relevant analyses looked at the 692 participants (about 47%) whose genetic results were considered “actionable,” meaning guidelines recommended a different medication or dose for them. Depression symptoms were measured with PROMIS questionnaires for both adults and children, with the Patient Health Questionnaire-8 (PHQ-8) as a secondary measure.
At three months, there was only a modest improvement in symptoms in both groups, with no meaningful difference between them and similar side-effect profiles. By six months, remission was higher in the genotype-guided group on the PROMIS measure (48% vs 39%), and also higher on the PHQ-8 (30% vs 21%).
Treatment changes reflected the guidance: at three months, 85% of patients in the genotype-guided group were taking a medication and dose aligned with their genetic profile, compared with 74% in the usual-care group. Among those whose results did not call for any change, there was no difference between groups.
“In this randomized clinical trial, genotype-guided prescribing of SSRIs did not improve control of depression symptoms at 3 months compared with usual care but was associated with higher depression remission rates at 6 months. These findings suggest a possible longer-term clinical benefit and indicate that future studies should focus on the durability and long-term impact of genotype-guided prescribing in the management of depressive symptoms,” the study authors concluded.
While the trial contributes to exploring genetic approaches to treating depression, it did not meet its primary outcome of improved symptoms at three months. The six-month remission finding was a secondary outcome, and the open-label design meant participants and clinicians knew which group was involved, with genotype results visible in health records, potentially influencing reporting or treatment decisions.
Other noted limitations included the absence of a formal major-depression diagnosis in the study design and the possibility that some participants had milder forms of depression. About 15% of actionable-genotype cases in the genotype-guided arm did not receive a gene-matched prescription at three months, and delays in implementing changes were not tracked.
The trial’s authors emphasise that using publicly available guidelines rather than proprietary algorithms was a strength, but they acknowledge that longer-term outcomes and durability of genotype-guided prescribing warrant further investigation.
