Lemon balm (Melissa officinalis) is a perennial flowering plant that belongs to the Lamiaceae or mint family. Other common names for lemon balm include common balm, balm or mint balm. The plant is native to South and Central Europe, as well as parts of the Mediterranean, Iran and Central Asia. The plant can reach a height of around 1.5 meters and in the summer it produces small white flowers. The plant gives off a mint scent from its leaves. Lemon balm has been used in traditional medicine as a treatment for memory disorders, gastrointestinal disorders, and sleep disturbance. The benefits of lemon balm in combination with valerian as a sedative and sleep aid has been demonstrated in healthy individuals where the combination of lemon balm and valerian was rated to be 33 % better than the placebo. This study reported no serious adverse effects from the herbal treatment. In another study, the combination of lemon balm and valerian was shown to be as effective as the benzodiazepine drug triazolam.
The ability of lemon balm to cause a calming effect in human has been investigated using healthy volunteers. Subjects received either 300 or 600 mg of lemon balm extract in single doses, or a placebo. The subjects were then exposed to a series of stressful tests. The 600 mg dose of lemon balm was significantly able to elevate the mood of the subjects and counteract the expected mood deteriorating effects of the stress test. The subjects taking 600 mg of lemon balm reported significant increases in calmness and alertness compared to the placebo. There was also a significant increase in the ability to accurately process the mathematical problems in the test at the 300 mg dose, compared to the placebo. Therefore lemon balm appears to show calming and mood elevating properties in healthy human subjects in response to the application of stressful conditions. The improvements in cognitive function suggest that at these doses the lemon balm was not inducing detrimental sleepiness in the subjects.
It is not clear how lemon balm is able to produce its calming, sedative and cognitive effects. However, lemon balm extract is known to contain a number of phytochemicals including monoterpenoid aldehydes, monoterpene glycosides as well as polyphenols including flavonoids and rosmarinic acid. These compounds may explain the antioxidant properties reported for the herb. This may suggest that some of the beneficial effects of the herb may come from a general antioxidant effect. However, extracts of the plant are also able to inhibit the monoamine oxidase (MAO) enzyme. This enzyme is involved in the breakdown of neurotransmitters including dopamine, serotonin and noradrenaline. By inhibiting this enzyme the extracts of lemon balm may be able to raise levels of these neurotransmitters in the brain. As low levels of these neurotransmitters are associated with depression and anxiety disorders, this may explain the mood elevating effects of the herb.
In a human study researchers investigated the effects of lemon balm on mood and cognition in healthy subjects. A single 300, 600 or 900 mg dose of lemon balm or a placebo was administered to healthy subjects and then a series of stressful tests were performed. Accuracy and attention was improved significantly in the subjects taking 600 mg of lemon balm. However, as the dose of lemon balb increased there were reductions in the memory functions of the subjects. Calmness was elevated most at the 300 mg dose of lemon balm. Therefore the cognitive and calmative functions of lemon balm may change with the dose administered. These results generally show that lemon balm is a mild calmative agent with some cognitive effects. However, it is not clear how lemon balm is able to have these cognitive enhancing effects. In has been suggested that the ability of lemon balm to improve cognitive function may stem from its ability to activate the cholinergic system in the brain through interaction with both muscarinic and nicotinic receptors.
Lemon balm extracts show specific cognitive enhancing effects, and these effects may be partly explainable by the ability of the herb to activate the cholinergic system in the brain. In this way they increase levels of the neurotransmitter acetylcholinesterase. However, this ability may differ between different batches of the herb. Evidence also suggests that extracts of lemon balm are able to inhibit the enzyme GABA transaminase. This enzyme is responsible for the breakdown of GABA in the brain. By inhibiting this enzyme, lemon balm may be able to potentiate the effects of GABA in neurones in the brain, and this would have an inhibitory effect on neuronal activity, producing an overall calming and sedative effect in the individual. GABA transaminase inhibitor drugs are used for this purpose to treat conditions including epilepsy and anxiety. Analysis of extracts of lemon balm indicate that rosmarinic acid and the triterpenoids ursolic and oleanolic acid may be responsible for this GABA transaminase inhibition.
It is known that activation of the cholinergic system is associated with improved cognition, and is this is one target of therapies aimed at improving the memory decline seen in Alzheimer’s disease. Therefore in another study, researchers screened a range of lemon balm samples to assess their ability to interact with cholinergic receptors. The sample with the highest ability to bind to cholinergic receptors was then assessed for its cognitive ability. Doses used in the study were at 600, 1000 and 1600 mg lemon balm. The results showed that at the highest dose of lemon balm produced the greatest improvements in overall cognitive function. The highest and middle doses also improved self-rated calmness in the individuals significantly compared to the lowest dose. As the calming and cognitive effects of lemon balm have been seen in a number of studies, but only one study demonstrated cholinergic binding ability, it is possible that some other mechanism partly explains the ability of lemon balm to modulate both mood and cognition.
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