Plant by Plant

Lemon Balm: Rosmarinic Acid, GABA, and a Stress Study

Lemon balm is Melissa officinalis, a lemon-scented plant in the mint family, Lamiaceae, and it's native to the Mediterranean (Mathews et al., 2024). Its leaves carry volatile oils, the compounds that evaporate off a crushed leaf, including citral, citronellal, geraniol and linalool. They also carry rosmarinic acid and two triterpenoids, oleanolic acid and ursolic acid (Mathews et al., 2024).

What rosmarinic acid does to GABA

Your brain uses a chemical messenger that slows nerve signals down. It's called GABA, short for gamma-aminobutyric acid. Mathews and colleagues describe how an enzyme called GABA transaminase breaks GABA down, so when something blocks that enzyme, GABA builds up instead of being broken down.

In 2009, Awad and colleagues made an extract of lemon balm leaves and found that it blocked GABA transaminase taken from rat brains. To find out which compounds were responsible, they split the extract into fractions, tested each one, and kept splitting the active fractions until they'd isolated three compounds: rosmarinic acid, ursolic acid and oleanolic acid. Rosmarinic acid accounted for most of the effect. At a concentration of 100 micrograms per milliliter it cut the enzyme's activity by 40%, and it made up about 1.5% of the dry weight of the leaves (Awad et al., 2009).

Awad's result came from a test tube. It shows what rosmarinic acid can do to the enzyme when the two meet directly, and it gives human studies a specific mechanism to look for.

The stress study

In 2004, Kennedy, Little and Scholey tested lemon balm on 18 healthy volunteers under stress. Each volunteer came in on three separate days, a week apart. On one day they took a lower dose of a standardized lemon balm extract, on another a higher dose, and on the third a placebo. Every person took all three, so each one was compared against themselves. That design is called a crossover. It was also double-blind, meaning neither the volunteers nor the researchers knew which dose was given on which day.

An hour after each dose, the volunteers did a 20-minute battery of four tasks running at the same time, built to put people under pressure in the lab. It's called the Defined Intensity Stressor Simulation. After the higher dose, the volunteers rated themselves calmer and less alert than after the placebo, which offset the drop in mood the tasks caused. After the lower dose, they did the math task faster with no loss of accuracy (Kennedy et al., 2004).

The authors concluded that lemon balm's potential to reduce the effects of stress deserves more study. Eighteen people is a small group, and each dose was a single one, so the study measured the hour after one dose. Daily use over weeks is a separate question.

Where the research stands

Mathews and colleagues reviewed the clinical work on lemon balm in 2024. They concluded that lemon balm shows promise as a calming agent, with effects on anxiety, mood, thinking and sleep quality, and that more large randomized controlled trials are needed. The two lines of research fit together: in a test tube, rosmarinic acid acts on the enzyme that breaks GABA down, and in the stress study, volunteers reported feeling calmer after lemon balm. Mathews and colleagues suggest measuring GABA directly in volunteers' brains with a type of brain scan called magnetic resonance spectroscopy, which is the step that would connect the two.

Go further

My Sleep & Stress guide has a chapter on lemon balm and a simple bedtime tea blend: kbaco.net/downloads/seasonal-sleep-stress

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