This Practice Note provides an introduction to the process of testing medicinal products in humans (known as clinical trials). It sets out the UK regulatory framework for clinical trials, explaining the changes introduced into UK regulation by the Medicines for Human Use (Clinical Trials) (Amendment) Regulations 2025 (UK CTR 2025), SI 2025/538. It further explores some practical considerations including how to apply for authorisation to conduct a clinical trial, how to conduct and conclude a clinical trial, how to prepare a clinical trial protocol and links to various clinical trial agreements (CTAs). It also discusses the various stages of clinical trials (referred to as phases I, II, III and IV), the parties involved, informed consent and the special rules relating to minors and incapacitated adults. Finally, it briefly considers clinical trials conducted outside the UK as well as related areas of law, including data protection for clinical trial data and personal data, clinical trial disclosure, and the research and Bolar exemptions in patent law. The UK and EU have different regulatory frameworks for clinical