Complex investigation on the effect of Thiourea, Galmet and Thiogalmet compositions on water status, intensity of photosynthesis, water use efficiency, growth and yield of ‘P458’ maize plants under conditions of natural humidity in field trials was performed. The beneficial effect of seed and foliage pre-treatment with Thiourea, Galmet and, in particular, the new chemical composition Thiogalmet on plants’ biological processes conditioning a better realisation of the physiological processes associated with plant growth and productivity was established. A significantly greater positive impact of Thiogalmet on the optimisation of hydration degree, water retention capacity, stomatal conductance for CO2/H2O, assimilation, water use efficiency, plant growth and productivity was recorded. There was an additive action of Thiourea and Galmet in the composition of the Tiogalmet preparation. Thiogalmet increased the yield per unit area and improved the commercial quality of the grain. Treating plants with Thiourea, Galmet and Thiogalmet ensured a 27.20, 52.08 and 68.20% yield increase, respectively, compared to the plants in the control variant. Therefore, a major effect was registered in the plants treated with the new composition. The obtained information demonstrates the possibility of mitigating the adverse effects of drought on the physiological response and production by applying antioxidants.