In this study, four perennial medicinal plant species, namely Convolvulus hystrix Vahl. (C. hystrix), Maerua oblongifolia Forssk. A. Rich. (M. oblongifolia), Cadaba glandulosa Forssk. (C. glandulosa), and Fagonia indica Burm. f. (F. indica), were analyzed for their primary metabolites (carbohydrates, amino acids, proteins, and proline) and secondary metabolites (phenolic compounds, flavonoids, saponins, alkaloids, and terpenoids) during the summer and winter seasons in Jeddah, Kingdom of Saudi Arabia (KSA). Additionally, the phytochemical composition of the plant species was analyzed using gas chromatography-mass spectrometry (GC-MS) in both seasons. M. oblongifolia exhibited higher levels of proline and amino acids in the summer but showed lower concentrations of soluble sugars, phenols, and saponins in the winter. During the summer, C. glandulosa displayed high levels of amino acids and alkaloids, whereas in winter, it recorded the lowest levels of soluble proteins. Meanwhile, F. indica exhibited its highest levels of proline and alkaloids during the winter season, while sugars, saponins, amino acids, and terpenoids peaked during the summer. Additionally, C. hystrix showed elevated concentrations of phenols, flavonoids, alkaloids, and terpenoids in the summer. GC-MS analysis revealed that fatty acids were the main constituents in the plant species, with the highest concentrations observed in M. oblongifolia, C. glandulosa, and F. indica during the summer, and in C. hystrix during the winter. Furthermore, C. glandulosa exhibited the persistence of therapeutic compounds like caryophyllene and vanillin in the winter. Overall, when collecting medicinal plants, it is essential to conduct a comprehensive investigation considering critical factors such as timing, developmental stage, fertilization techniques, protective measures, and irrigation practices to maximize yield.