Application of the Principle of Lex Favor Reo in the Decision of Narcotics Crimes during the Transition Period of the National Criminal Code (Study of the Supreme Court's Cassation Decision in 2026)

Law Number 1 of 2023 concerning the Criminal Code (National Criminal Code), concurrent with Law Number 1 of 2026 concerning Criminal Adjustments, came into effect on January 2, 2026, giving rise to intertemporal legal issues (transitoir strafrecht) in narcotics crimes where the tempus delicti occurred before that date but were only tried thereafter. Article 3 Paragraph (1) of the National Criminal Code stipulates the principle of lex favor reo as a guideline for resolving intertemporal legal conflicts, but its application in Supreme Court cassation decisions demonstrates a variety of inconsistent legal considerations, thus giving rise to issues of consistency and legal certainty. This study aims to examine the philosophical basis for the application of the lex favor reo principle, its regulations according to the National Criminal Code and the Narcotics Law, and its application in the Supreme Court's cassation decision in 2026. The results of the study indicate that the philosophical basis of the lex favor reo principle is derived from the values ​​of Pancasila justice and the guarantee of fair legal certainty in Article 28D Paragraph (1) of the 1945 Constitution; normatively, this principle is regulated in Article 3 Paragraphs (1) and (7) of the National Criminal Code which are directly related to changes in the structure of narcotics criminal threats after the Criminal Adjustment Law from cumulative to alternative without a specific minimum limit; In practice, the three cassation decisions reviewed consistently apply this principle ex officio to mitigate the sentences of drug defendants, albeit with varying degrees of legal reasoning. Decision Number 463 K/Pid.Sus/2026 demonstrates the most systematic application through a quantitative comparison of the old and new criminal penalties.