This book examines the regulatory framework for untested and unapproved uses (off-label uses) of medicines in the EU, UK, and USA. Before reaching patients, medicines are extensively tested by manufacturers and approved by regulators to minimise the risk of adverse reactions. However, physicians can prescribe pharmaceuticals for off-label uses, widespread in paediatrics, oncology, rare diseases and, more recently, in treatment for Covid-19. While off-label uses may offer hope, they may also expose patients to risks and uncertainties. Clarification is therefore needed to improve the protection of patients' rights while enhancing legal certainty for health actors. To this end, this work clarifies the regulatory mechanisms and litigation trends concerning off-licence prescriptions in these jurisdictions. It assesses how traditional, prevention-driven regulatory and civil liability rules are being adapted to tackle potential risks and scientific uncertainty. The book outlines the applicable regulations, as well as considering Brexit's impact on off-label policies in the UK, and EU and national off-label policies in the context of the fight against the Covid-19 pandemic. It also explores under what conditions physicians, manufacturers, or regulators must compensate patients injured by untested prescriptions. The book will be an essential resource for researchers, academics and policy-makers working in the areas of medical law and ethics, public health law, pharmaceutical law and private comparative law.