Berg et al. evaluated the cytotoxicity and mutagenicity of GA in male Chinese hamster lung fibroblasts (V79 cells)23. Their results showed toxicity on cells grown in DMEM supplemented with 10% FBS after 24 hours in GA concentrations above 50 µM, with no mutagenic effect. Ahlemeyer et al. reported that 500 µM GA induced neuronal death and activated protein phosphatase type-2C in chick embryonic neurons growing in DMEM with 20% FBS12. B.M Hausen, evaluated the sensitizing capacity of GA in guinea pigs, determining 1000 ppm (2.886 mM) GA as safe to avoid inducing an allergic reaction24. Viral infections of permissive cells are regularly performed in 199 or MEM medium supplemented with 1% or 2% FBS. However, when we tested the activity and toxicity of GA on the cells used in our research, we also incubated the cells with GA in the cells’ recommended growth medium (see results and Fig. S1). The results indicated that the activity and toxicity of GA is affected by the serum concentration in the medium. We concluded that GA interacts with serum factors, which lowers its antiviral activity, and researchers using GA should address this issue in future experiments. In vivo experiments in an animal model are needed to assess the actual therapeutic antiviral effect and cytotoxicity of GA.