Valerenic acid is a key active constituent of the valerian root (Valeriana officinalis), which has a long history of traditional use as a herbal remedy for promoting relaxation and sleep. The traditional use of valerian relates to its calming effects, which are believed to be mediated by interactions with the central nervous system, particularly through modulation of gamma-aminobutyric acid (GABA) receptors. While the parasympathetic nervous system is associated with "rest and digest" functions, direct evidence linking valerenic acid specifically to support or modulation of the parasympathetic nervous system is limited. Most of the available research and historical use focus on the broader sedative and anxiolytic properties of valerian and its components. Some preclinical studies have shown that valerenic acid can enhance GABAergic activity, contributing to relaxation and potentially supporting the body's ability to shift toward parasympathetic dominance. However, clinical studies in humans are mixed, with some suggesting mild benefits for sleep and anxiety, but without direct measurement or confirmation of parasympathetic nervous system activity. In summary, while there is a traditional basis for the use of valerenic acid (via valerian root) to promote relaxation, scientific evidence directly supporting its use for parasympathetic nervous system function is limited, and the justification for such use remains primarily traditional.