## Treatment-Resistant Depression: Defining the Discriminator **Key Point:** Treatment-Resistant Depression (TRD) is operationally defined by failure to achieve adequate response to sequential trials of antidepressants at adequate doses and durations, not by symptom profile or patient demographics. ### Operational Definition of TRD **High-Yield:** The most widely accepted definition (Thase & Rush criteria) requires: 1. Failure of response to **at least 2 adequate antidepressant trials** (different classes preferred) 2. Each trial at **therapeutic dose** for **4–6 weeks minimum** 3. **Adequate adherence** confirmed 4. Absence of confounding factors (substance use, medical comorbidity, inadequate psychotherapy) **Clinical Pearl:** TRD affects 30–40% of patients with MDD and carries implications for treatment escalation: augmentation strategies (lithium, atypical antipsychotics), combination therapy, or neuromodulation (ECT, rTMS, ketamine). ### Comparison: TRD vs. Non-Resistant MDD | Criterion | Non-Resistant MDD | Treatment-Resistant Depression | | --- | --- | --- | | **Response to 1st antidepressant** | Remission/response achieved | No response | | **Number of failed adequate trials** | 0–1 | ≥2 | | **Dose adequacy** | Therapeutic | Therapeutic | | **Duration per trial** | 4–6 weeks | 4–6 weeks each | | **Symptom profile** | Variable | Variable (not discriminatory) | | **Age/gender** | Any | Any (not discriminatory) | **Warning:** Do not confuse TRD with simply a longer episode duration. A patient with a 12-month episode who responds to the first antidepressant trial is NOT treatment-resistant; conversely, a patient with a 4-week episode who has failed two adequate trials IS treatment-resistant. **Mnemonic:** **TRAD** = **Two Resistant Antidepressant Doses** (at least 2 adequate trials define TRD).
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