Lemon balm (Melissa officinalis) has been traditionally used for its calming effects, and in recent years, scientific studies have investigated its impact on the gamma-aminobutyric acid (GABA) system, which is the primary inhibitory neurotransmitter system in the central nervous system associated with stress and anxiety modulation. Several in vitro and clinical studies suggest that compounds in lemon balm, particularly rosmarinic acid, can inhibit GABA transaminase, an enzyme responsible for the breakdown of GABA. This inhibition may lead to increased GABA levels in the brain, thereby contributing to the herb’s anxiolytic and calming effects.

Human clinical trials, while limited in size and scope, have shown that lemon balm extracts can reduce self-reported anxiety and improve mood, possibly via modulation of the GABA system. For example, a randomized, placebo-controlled trial found acute administration of lemon balm extract led to increased calmness and reduced alertness in healthy volunteers. However, these studies often use combination products or relatively high doses, and the precise mechanism—while plausible—has not been fully elucidated in humans. The evidence is promising but not conclusive, justifying a moderate evidence rating.