Lost in translation: how to interpret data from MDD clinical trials and observational studies to inform clinical practice?

“Lost in translation” names the gap between population-level evidence and individual clinical care. A first step is recognizing that depression is a heterogeneous disorder whose conceptualization has shifted historically. Although the endogenous–exogenous distinction has largely disappeared from contemporary thinking, the clinical question it indexed remains consequential.

Large-scale randomized controlled trials (RCTs) and meta-analyses achieve comparability through diagnostic uniformity and protocolized outcomes. Yet this uniformity can compress heterogeneity in course, comorbidity, symptom structure, and meaning. Observational studies, despite greater susceptibility to confounding, can complement trials by capturing real-world trajectories, adherence, functional outcomes, and patient-reported change, thereby widening the evidential field. In some cases they provide primary evidence– for example, in detecting less common adverse effects or informing care for populations underrepresented in RCTs, such as pregnant or breastfeeding women.

Clinical guidelines, including those for treatment-resistant depression, are typically produced by national bodies that translate RCT-centered hierarchies into graded recommendations and algorithms. However, these documents encode abstraction as well as evidence, and their operational definitions do not always map cleanly onto clinical reality. At the conceptual core lies the risk of epistemological transgression: importing RCT averages uncritically into a singular case.

Translation therefore requires case conceptualization: a theory of the patient’s maintaining factors and treatment targets. Similar mean effects in RCTs do not imply interchangeability in practice, where tolerability, symptom profiles, adherence, and impacts on functioning and quality of life differ. Efficacy evidence is necessary but not sufficient; better practice emerges from integrating RCT findings with observational evidence and a phenomenological orientation toward embodied psychopharmacology.