Prediction of 12-Week Remission in Patients With Depressive Disorder Using Reasoning-Based Large Language Models: Model Development and Validation Study.

Background: Depressive disorder affects over 300 million people globally, with only 30% to 40% of patients achieving remission with initial antidepressant monotherapy. This low response rate highlights the critical need for digital mental health tools that can identify treatment response early in the clinical pathway. Objective: This study aimed to evaluate whether reasoning-based large language models (LLMs) could accurately predict 12-week remission in patients with depressive disorder undergoing antidepressant monotherapy and to assess the clinical validity and interpretability of model-generated rationales for integration into digital mental health workflows. Methods: We analyzed data from 390 patients in the MAKE Biomarker discovery study who were undergoing first-step antidepressant monotherapy with 12 different medications, including escitalopram, paroxetine, sertraline, duloxetine, venlafaxine, desvenlafaxine, milnacipran, mirtazapine, bupropion, vortioxetine, tianeptine, and trazodone, after excluding those with uncommon medications (n=9) or missing biomarker data (n=32). Three LLMs (ChatGPT o1, o3-mini, and Claude 3.7 Sonnet) were tested using advanced prompting strategies, including zero-shot chain-of-thought, atom-of-thoughts, and our novel referencing of deep research prompt. Model performance was evaluated using balanced accuracy, sensitivity, specificity, positive predictive value, and negative predictive value. Three psychiatrists independently assessed model outputs for clinical validity using 5-point Likert scales across multiple dimensions. Results: Claude 3.7 Sonnet with 32,000 reasoning tokens using the referencing of deep research prompt achieved the highest performance (balanced accuracy=0.6697, sensitivity=0.7183, and specificity=0.6210). Medication-specific analysis revealed negative predictive values of 0.75 or higher across major antidepressants, indicating particular utility in identifying likely nonresponders. Clinical evaluation by psychiatrists showed favorable mean ratings for correctness (4.3, SD 0.7), consistency (4.2, SD 0.8), specificity (4.2, SD 0.7), helpfulness (4.2, SD 1.0), and human likeness (3.6, SD 1.7) on 5-point scales. Conclusions: These findings demonstrate that reasoning-based LLMs, particularly when enhanced with research-informed prompting, show promise for predicting antidepressant response and could serve as interpretable adjunctive tools in depressive disorder treatment planning, although prospective validation in real-world clinical settings remains essential.