The medicinal plant Jatropha curcas exerts beneficial effects against ethanol toxicity in humans. In this work, we investigated the protective effect of three extracts (ethanol [Et], vegetal glycerin [VG], and propylene glycol [PG]) of J. curcas leafs against Et‐induced damage in human peripheral blood mononuclear cells. The cytotoxicity of the extracts alone or in combination with each other in mononuclear cells was also assessed. A thermodynamic and kinetic analysis of the protection assumed that the cells were in a metastable equilibrium of growth and death, and the mass action of the extracts was used to determine the optimal concentration for each extract. The PG and VG extracts were cytotoxic, with an efficiency index of protection (η) of approximately −20% and −41%, respectively. By contrast, η values of ∼220% were observed for Et extracts (0.625% vol/vol) and combined extracts (Et + PG) at concentrations of (0.375 + 0.250)% and (0.5 + 0.5)%, respectively. These results identify J. curcas as a promising source of bioactive compounds and show that appropriate modeling can provide a powerful system for determining the optimal conditions for drug action.