C. AMOS-ISEI

Insanity defence remains one of the most complex and controversial doctrines in criminal law. At its core, it presents a legal mechanism through which a person suffering from a mental disorder at the time of committing an offence may be excused from criminal liability. This research explores the evolution of the insanity defence, with a particular focus on the M’Naghten Rules, which were formulated in 1843 following the landmark case of Daniel M’Naghten. These rules have since become the foundational legal standard for determining criminal responsibility in cases involving mental illness across many common law jurisdictions, including Nigeria. The study traces the historical development of the insanity defence, analysing its philosophical underpinnings, judicial interpretations, and practical application. It
critically assesses the doctrinal relevance of the M’Naghten Rules within contemporary legal and psychiatric contexts, especially in light of modern understandings of mental illness and cognitive incapacity. Using the doctrinal method, this work examines primary sources such as statutory provisions and case law, alongside secondary materials like textbooks, journal articles, and comparative analyses from other jurisdictions such as the United Kingdom, the United States, and Canada. A key focus of the research is how Nigerian courts have applied the M’Naghten Rules within the frameworks of the Criminal Code and Penal Code, and whether these applications align with evolving human rights standards and medical insights. The study concludes by identifying limitations in the current legal framework and proposes reforms aimed at achieving a more just and medically accurate approach to criminal responsibility in cases involving mental disorders