Implication for health policy/practice/research/medical educationOxidative stress is caused by an imbalance in production of reactive oxygen and the biological ability to detoxify the reactive intermediates or repair the resulting damage. Herbal medicines commonly fight these complications with their antioxidant properties. However, it should be noted that herbal drugs extracts are abundant sources of polyphenols and these compounds are unstable and might be subjected to polymerization. Thus, it is essential to check that the observed biological properties are not due to polymerization of phenolic compounds.