Summary: Severe treatment recalcitrant atopic dermatitis (AD) is a debilitating condition with substantial population impact. Dermatology has experienced the emergence of targeted immuno-modulating drugs (IMDs) that have unprecedented efficacy in treating AD. Their optimal use is still unknown because their safety remains insufficiently characterized. A range of serious side effects are conceivable based on the immunologic pathways although it is unlikely that they will all play out in clinical practice. Quantifying or refuting these adverse effects is critical for a clinical benefit-risk assessment and personalized treatment decisions. Existing trials have not answered these questions and are unlikely to address them in the near future. The resulting uncertainty has led to both overly restrictive but also aggressive prescribing of highly efficacious IMDs and this proposal aims to close this glaring knowledge gap. We propose a population-based prospective drug safety monitoring system leveraging existing data sources that shortens the time to insights and provides high validity findings through advanced causal inference methods. Analyses of longitudinal healthcare databases cover a source population of >78 million Americans and include commercially insured and Medicaid beneficiaries. New and urgently needed safety insights will reflect clinical practice, including populations typically excluded from RCTs, like children, women in reproductive age, patients with complex diseases, minority populations, and patients with existing risk factors. The size of the claims data source increases statistical power and the linkage to electronic health records in subsets improves clinical depth. We use causal inference methods that demonstrated high validity in pilot data and complement them with a novel data mining approach to identify unsuspected events. Analyses are done with highest transparency and reproducibility to support clinical decision making. This project’s finding on the optimal use of IMDs in clinical practice will lead to more targeted prescribing and benefit large patient groups, including populations underrepresented in RCTs: children, older adults, pregnant women, racial minorities, patients with pre-existing infections, cancers, VTE and others. This project is highly innovative as it will generate directly applicable clinical insights on the safe and targeted use of new immuno-modulating drugs (IMDs) to treat atopic dermatitis. Leveraging existing claims data sources with added EHR data it builds on novel methods for causal inference to mitigate biases arising in real- world data analyses in dermatology. The expedited evidence generation via the proposed prospective monitoring system combined with our track record in pharmacoepidemiologic analyses, this research will efficiently close knowledge gaps for optimal IMD use in many underrepresented and high-risk patients.