This thesis investigates the impact of regulatory policies on over-the-counter (OTC) and prescription drug categorization through a comparative study between Nigeria and Ireland, with the aim of addressing the issue of irrational drug use. The research addresses several key questions: What are the current regulatory policies and practices regarding drug categorization in Nigeria and Ireland? How do these frameworks compare in terms of classification criteria, approval processes, and international standards? How do variations in availability and accessibility of OTC and prescription drugs impact their utilization and influence patterns of drug misuse and abuse? Additionally, the study explores correlations between regulatory differences, drug classifications, and the prevalence of irrational drug use in both countries, aiming to provide recommendations for enhancing regulatory frameworks. A mixed-methods approach was used for the purpose of the research, involving document analysis, thematic analysis and surveys distributed to consumers, healthcare professionals, and regulatory officers in both countries. The study assesses consumer perceptions, self-medication practices, and healthcare professionals experiences with drug categorization and regulatory policies. The result analysis revealed key similarities in regulatory policies on OTC and prescription drug categorization between both countries, including classification criteria, approval processes, and recognition of international standards. Key differences include detailed legal supply categories and criteria for OTC classification; Nigeria’s criteria focus primarily on established efficacy and safety, with less emphasis on factors like the presence of controlled substances and the risk of medicinal abuse. Primary research findings showed significant differences in consumer familiarity with drug categories, perceptions of regulatory effectiveness, and self-medication behaviors between Nigeria and Ireland. In Ireland, 47% of respondents perceive regulatory policies as very effective, compared to 12% in Nigeria. Also, 23% of Irish respondents reported obtaining medications OTC, while only 14% of Nigerian respondents did the same. Selfmedication is prevalent in both countries, with 7% of Irish respondents and 5% of Nigerian respondents selfmedicating very frequently. However, 21% of Nigerian respondents reported experiencing side effects from selfmedication compared to 16% in Ireland, indicating a higher risk of adverse health outcomes in Nigeria. Healthcare professionals in both countries report encountering patients with side effects from self-medication, with 68% of Irish and 67% of Nigerian healthcare workers noting such cases. This highlights the need for regulatory interventions. From the feedback from Regulatory officials in Nigeria, they suggested improvements in the implementation and enforcement of existing policies, while also advocating for clearer drug categorization criteria and stricter control measures to prevent the abuse of OTC drugs. The Chi-square test of independence was used to examine the association between regulatory policies (independent variable) and irrational drug use (dependent variable). For Nigeria, there was no statistically significant association between how individuals typically obtain their medications and whether they have experienced side effects from self-medication (p = 0.181). Meanwhile, in Ireland, a significant association was found (p =< .001), indicating a strong relationship between medication acquisition methods and the occurrence of side effects. Furthermore, in Nigeria, a significant association was found between familiarity with drug categorization and the frequency of medication use without consulting a healthcare professional (p < .001), whereas no significant association was observed in Ireland (p = 0.057). This suggests that in Nigeria, awareness of drug classifications influences self-medication behavior, whereas other factors may play a more significant role in Ireland. Based on these findings, the study recommends revising drug categorization criteria to be more rigorous in Nigeria to enhance patient safety and promote rational drug use. Recommendations for both countries to enhance regulatory frameworks to prevent irrational drug use and safeguard public health includes public education campaigns, strengthening regulatory oversight, improving access to healthcare services, and empowering pharmacists to play a more active role in patient education and counseling regarding medication use. These measures align with global best practices, enhancing medication quality and promoting of course, rational drug use