Prunus spinosa L. (blackthorn) is a valuable source of bioactive compounds, including flavonoids, anthocyanins, phenolic acids, vitamins, and minerals, which confer important antioxidant, antibacterial, and anti-inflammatory properties. This comparative review synthesizes experimental data from our previously published research and from the global literature to highlight the phytochemical composition, variability, and potential application prospects of these fruits. The diversity of results obtained in terms of total phenolic content (TPC), total anthocyanin content (TAC), and total flavonoid content (TFC) and biological activities can be explained by the variability of the extraction method, as well as the geographical origin of Prunus spinosa L., and demonstrates its relevance for health applications. The results of this comprehensive review revealed an increased potential of Prunus spinosa L. extracts for phytotherapeutic, nutraceutical, and functional product applications.