Lemon balm does appear to increase serotonin activity in the brain, though the evidence comes primarily from animal studies rather than direct measurements in humans. Its key active compound, rosmarinic acid, has been shown to boost both serotonin levels and serotonin signaling in brain tissue. But the full picture is more nuanced than a simple yes or no, because lemon balm works through multiple brain pathways at once, and its serotonin effects may not be the main reason it helps with mood and anxiety.
How Lemon Balm Affects Serotonin
The strongest link between lemon balm and serotonin centers on rosmarinic acid, the most abundant active compound in the plant. Animal research has shown that rosmarinic acid increases serotonin levels in the brain and enhances signaling through serotonin’s postsynaptic receptors, the docking sites where serotonin delivers its mood-regulating messages. In rats showing depressive behavior, rosmarinic acid raised levels of both serotonin and its main metabolite (a breakdown product that indicates more serotonin is being used), suggesting the brain was both producing and actively cycling more serotonin.
One way rosmarinic acid may accomplish this is by influencing monoamine oxidase, the enzyme family responsible for breaking down serotonin and other mood-related neurotransmitters. Rosmarinic acid can alter the expression and activation of both major forms of this enzyme (MAO-A and MAO-B). This is loosely similar to how some prescription antidepressants work, though rosmarinic acid’s inhibition of these enzymes requires relatively high concentrations compared to pharmaceutical drugs. So while the mechanism exists, it’s not as potent as a targeted medication.
Interestingly, earlier research suggested that lemon balm’s antidepressant-like effects might not depend on serotonin reuptake or monoamine oxidase at all. More recent studies have pushed back on that, showing that the monoamine system is indeed involved. The current understanding is that serotonin modulation is one real piece of lemon balm’s effects, but not the only one.
GABA: The Other Major Pathway
If you’re researching lemon balm for anxiety or stress, its effects on GABA are arguably more relevant than its serotonin activity. GABA is the brain’s primary calming neurotransmitter, and lemon balm has a well-documented ability to increase GABA levels through a specific mechanism: it inhibits an enzyme called GABA transaminase, which normally breaks GABA down. By slowing this breakdown, lemon balm allows more GABA to remain active in the brain.
Rosmarinic acid is again the star player here. In laboratory testing, it accounted for about 40% inhibition of GABA transaminase activity at a tested concentration. Two other compounds in lemon balm, ursolic acid and oleanolic acid, also contribute to this effect. This GABA pathway is a recognized drug target for treating anxiety, epilepsy, and related neurological conditions, which gives some pharmacological credibility to lemon balm’s traditional use as a calming herb.
GABA and serotonin systems are not entirely separate. They interact in the brain, and boosting GABA activity can indirectly influence how serotonin circuits behave. This means that even lemon balm’s GABA effects could contribute to changes in serotonin signaling, making it difficult to isolate one pathway from the other in practice.
What This Means for Mood and Anxiety
The combination of serotonin modulation and GABA enhancement helps explain why lemon balm has shown antidepressant and anxiolytic (anxiety-reducing) effects in animal models. In forced swimming tests, a standard method for evaluating antidepressant potential in rats, lemon balm extract reduced depressive-like behavior through its action on the serotonergic system. Both single-dose and repeated-dose treatments produced effects.
For humans, the practical translation is less precise. No clinical trials have directly measured serotonin levels in people taking lemon balm, because doing so would require spinal fluid samples or PET brain scans. What human studies have measured are outcomes like self-reported anxiety, calmness, and stress, and lemon balm generally performs well on those measures. Whether those benefits come primarily from serotonin changes, GABA changes, or both working together remains an open question.
Using Lemon Balm Alongside SSRIs
If lemon balm increases serotonin activity, a natural concern is whether it’s safe to combine with SSRI antidepressants, which also raise serotonin levels. Too much serotonin can cause a dangerous condition called serotonin syndrome. According to drug interaction databases, no formal interactions have been identified between lemon balm and common SSRIs like sertraline (Zoloft). This likely reflects the fact that lemon balm’s serotonin effects are relatively mild compared to pharmaceutical drugs.
That said, the absence of a documented interaction isn’t the same as proof of safety. The combination simply hasn’t been rigorously studied. If you’re taking an SSRI or any other serotonin-affecting medication, it’s worth mentioning lemon balm use to your prescriber, especially at higher supplemental doses rather than the small amounts found in herbal tea.
How to Get the Active Compounds
The serotonin and GABA effects described in research depend heavily on rosmarinic acid content, which varies widely between lemon balm products. A cup of lemon balm tea contains far less rosmarinic acid than a standardized extract capsule. Most clinical research on mood outcomes has used concentrated extracts rather than tea, typically in doses ranging from 300 to 600 mg per day, though study designs vary considerably.
Lemon balm can produce noticeable calming effects relatively quickly. Some studies have observed changes in mood and alertness within one to three hours of a single dose, suggesting that the GABA pathway in particular kicks in fast. Longer-term serotonin-related effects, like improvements in depressive symptoms, would likely require consistent daily use over weeks, similar to how pharmaceutical antidepressants need time to reshape neurotransmitter patterns.
If you’re choosing a supplement specifically for its serotonin or mood-related properties, look for products that list rosmarinic acid content or are standardized to a specific percentage of this compound. Whole-leaf preparations and teas still contain the active compounds but in lower and less predictable amounts.