In this study, the total phenolic content, the antioxidant activity and toxicity of selected Greek medicinal aromatic namely Melissa officinalis L., Origanum vulgare L., Origanum dictamnus L., Salvia officinalis L. and Hyssopus officinalis L., were investigated under three different extraction processes. Among the plants studied, Melissa officinalis L. showed the highest values in total phenolic content (0.985 ± 0.001 mg caffeic acid/mL) and antioxidant activity (6.61 ± 0.04 mol Trolox/mL) independently of the extraction process. Toxicity evaluation of the infusions prepared in concentrations contained in commercial portions showed that inhibition values of Origanum vulgare L. and Origanum dictamnus L. were greater than 20% thus further research is necessary. Although toxicity of plant extracts examined is not correlated to their total phenolic content and antioxidant activity, it was linked to the interaction of water soluble and volatile organic compounds. Interaction of water soluble and volatile organic compounds was evaluated through the estimation of synergism ratios (SR), where Origanum vulgare L., presented the maximum synergism (SR = 4.2) in toxicity.
