Substances have been used for medicinal, recreational, and enhancement purposes by numerous population groups since ancient times. This practice is as old as humankind itself with alcohol use in South Africa for instance dating back 70 000 years. Regulation of some substances has now become standard practice due to their harmful and deleterious effects, increasing the risk to the user and society, which includes the educational, workplace and sports environment. Regulation involves enlisting of substances and testing for these prohibited substances in humans to assess compliance. Such a program has to be ethically sound, legally correct and scientifically accurate. Prohibited substance regulation and testing in humans can be seen as a biomedical intervention on an individual which may violate the right to privacy, dignity, autonomy and freedom to use substances for medicinal, recreational and enhancement purposes. The field is flawed with ethical dilemmas that can be solved by employing the principalism approach, which involves respect for autonomy, nonmaleficence, beneficence and justice. The obtainment of voluntary free informed consent, as a prerequisite for respect for autonomy is essential before a prohibited substance test on an individual is initiated. The author suggests that ethical oversight be instituted by statute, at a standard equivalent to that of ethical clinical research which is aligned with the Nuremberg code. It was also suggested that the professionals involved in the administration of prohibited substance regulation and testing programs should be registered with a professional council to comply with minimum standards of education and professionalism. International prohibited substance regulation and testing programmes related to the workplace as an example of foreign law (SAMHSA), and sports doping (WADA) as an example of international law, were studied and evaluated against the relevant provisions of the Constitution of the Republic of South Africa (CSA) and statutes such as the Occupational Health and Safety Act and the Protection of Personal Information Act. The relevant sections in the CSA revolved mainly around respect for privacy, dignity, autonomy, freedom and equality. It was found that the prohibited substance regulation and testing policy was essential in all settings to provide legal certainty for subjects and administrators. The constitutional right to just administrative action is of vital importance for these policies which have to function in a quasi-judicial environment, also based on the principle of “separation of powers”. The legal implications of the recent legalisation of cannabis on the workplace and other safety-sensitive environments were assessed and it was concluded that organisations still had an obligation to regulate, and to test for the active constituent (_9-tetrahydrocannabinol or THC) in their employees, due to its impairment potential that increases the risk to the health and safety of others. It was also suggested that the relevant legislation, such as the Occupational Health Act be changed to include threshold concentrations or cut-off concentrations in biofluids which mark the onset of impairment. A cut-off concentration of 2 ng/mL in blood was suggested for THC, and the use of oral fluid and urine as matrices for testing was discussed due to the invasiveness of blood sampling. Current issues in South Africa is addressed from a forensic toxicology perspective. The use of the hypergeometric distribution, based on sampling without replacement was suggested as a means to obtain the minimum number of subjects to be selected from a group within a specified level of confidence. Observational and chemical strategies to identify drug users were reviewed. A strategy to evaluate drug screening devices was proposed and applied to typical devices currently on the market in South Africa. / Thesis (DPhil)--University of Pretoria, 2019. / Public Law / DPhil / Unrestricted