Ocimum tenuiflorum L. (syn. Ocimum sanctum L.), commonly known as holy basil or tulsi, is an aromatic medicinal plant widely used in traditional systems of medicine across South Asia. Its biological properties have been associated with a chemically diverse group of constituents, including phenolic acids, flavonoids, terpenoids, essential-oil components and other specialized metabolites. This review critically discusses the phytochemical composition of Ocimum tenuiflorum, factors affecting extraction and analytical recovery, and commonly applied methods for evaluating antioxidant activity. Particular attention is given to the relationship between plant material, solvent polarity, extraction conditions, chemical profiling and assay selection. In vitro assays such as DPPH, ABTS, ferric-reducing antioxidant power (FRAP) and oxygen-radical absorbance capacity (ORAC) provide complementary rather than interchangeable estimates of antioxidant behaviour. Results reported across studies are difficult to compare when plant provenance, chemotype, processing, extraction yield, concentration units and assay protocols are not adequately described. The review identifies recurring methodological limitations, including overreliance on a single antioxidant assay, incomplete reporting of extract composition, and the tendency to infer biological efficacy from chemical assays alone. Improved standardization, chromatographic characterization, appropriate controls and carefully designed biological studies are needed to establish reproducible relationships between phytochemical composition and antioxidant effects. The evidence supports Ocimum sanctum L as a promising source of bioactive compounds, while also indicating that claims of therapeutic effectiveness require evidence beyond in vitro antioxidant measurements.