The foothill pastures of the Kashkadarya basin and the Zarafshan range constitute a substantial reservoir of medicinal flora with considerable pharmaceutical potential. This study evaluated the total antioxidant, flavonoid, and vitamin C contents of eight medicinal plant species, principally Melissa officinalis, Mentha longifolia, and Origanum vulgare, across three phenological stages (spring, summer, and autumn), using high-performance liquid chromatography (HPLC) and spectrophotometric analysis. The study sought to establish optimal harvesting periods for industrial raw-material collection. All quantitative data had them expressed in SI-compliant units (mg/100 g); seasonal differences entailed assessment using one-way analysis of variance(ANOVA) with Tukey’s post-hoc test (P < 0.05, n = 3). Melissa officinalis attained the highest antioxidant content at the vegetative stage in spring (1170.0 mg/100 g), whereas Mentha longifolia (1050.0 mg/100 g) and Origanum vulgare (1020.0 mg/100 g) peaked during summer flowering. Flavonoid content peaked in summer for most species, with Peganum harmala showing the highest accumulation (352.5 mg/100 g). Vitamin C concentration was highest in spring in Mentha longifolia (121.0 mg/100 g). These results identify Melissa officinalis, Mentha longifolia, and Origanum vulgare as a ‘high-potential triad. ‘It indicates that pharmaceutical enterprises and raw-material collectors should schedule harvesting of Melissa officinalis in spring and Mentha longifolia and Origanum vulgare in summer to maximize antioxidant yield.

Keywords: Medicinal plants, antioxidants, Kashkadarya basin, seasonal dynamics, Melissa officinalis, Mentha longifolia, Origanum vulgare, green pharmaceuticals, biologically active food supplements or BAFS

Key findings: Melissa officinalis showed the highest antioxidant activity in spring (1170.0 mg/100 g), while Mentha longifolia (1050.0 mg/100 g) and Origanum vulgare (1020.0 mg/100 g) were leading during summer flowering.