The Thai Drug Act 1967 regulates private pharmacies in Thailand, but violations are common. Effective enforcement is vital because pharmacies are the main drug distribution channel and have direct contact with consumers. However, independent studies suggest that there are wide discrepancies in regulation - and that the number of prosecuted cases does not reflect the number of violations that actually occur. It seems that the reason for this discrepancy is that the Thai Food and Drug Administration (TFDA) inspectors do not fully exercise their authority in enforcing the Thai Drug Act 1967. This study aimed to seek out the reasons for this discrepancy by exploring the Act, the regulatory management system and TFDA inspectors' views and attitudes. Documentary analysis and semi-structured interviews were the two main methods used to collect data. Interviewees were recruited from current and former inspectors and policy makers in the TFDA. There were three main findings. First, there is friction between the principle of a formal legalistic approach and the practice of the flexible approach used by the TFDA in enforcement. Second, interviews suggest that inspectors do not wholeheartedly enforce the Drug Act 1967 because the majority view the Act as unrealistic and impractical, and perceive that sanctions are not proportional to the harms caused. In other words, they feel that most of the sanctions are too severe. Third, inspectors described a number of obstacles to the exercise of their authority, resulting from business pressures, professionalism and the working process in the TFDA enforcement system. These constraints result in inspectors using unofficial methods (such as verbal warning) rather than fully using the sanctions available to them. This has led to under-enforcement and the erosion of the deterrence effect created by the Act.