Systematic reviews and meta-analyses represent the uppermost ladders in the hierarchy of evidence. Systematic
reviews/meta-analyses suggest preliminary or satisfactory clinical evidence for agnus castus (Vitex agnus castus)
for premenstrual complaints, flaxseed (Linum usitatissimum) for hypertension, feverfew (Tanacetum

Herbal medicines are mixtures of more than one active ingredient. The multitude
of pharmacologically active compounds obviously increases the likelihood of
interactions taking place. Hence, the likelihood of herb–drug interactions is
theoretically higher than drug–drug interactions, if only because synthetic drugs