Lemon balm: Background. Actions

2010

Common Name

Lemon balm

Other Names

Balm mint, bee balm, blue balm, common balm, cure-all, dropsy plant, garden balm, sweet balm

Botanical Name / Family

Melissa officinalis (family Labiatae)

Plant Part Used

Aerial parts

Historical Note

Lemon balm was used in ancient Greece and Rome as a topical treatment for wounds. In the Middle Ages it was used internally as a sedative and by the 17th century, English herbalist Culpeper claimed it could improve mood and stimulate clear thinking. Nowadays, it is still used to induce a sense of calm and help with anxiety, but is also added to cosmetics, insect repellants, furniture polish and food.

Chemical Components

Flavonoids, phenolic acids, tannins, triterpenes, essential oil and sesquiterpenes. Of note, the herb contains citronellal, caffeic acid, eugenol, rosmarinic acid and choline. Growing and harvesting methods have a major influence on the amount of volatile oil present in the leaves. It has been found that the oil content in the herb is highest in the top third and lowest in the bottom two-thirds.

Lemon balm: Main Actions

ANXIOLYTIC AND SEDATIVE

Over the years, a number of studies involving rodents have suggested specific anxiolytic or sedative effects. More recently, a double-blind placebo-controlled study has confirmed anxiolytic activity is clinically significant for lemon balm essential oil. In 2005 a double-blind, placebo-controlled, randomised, crossover trial of a whole extract of lemon balm (300 and 600 mg) in 18 healthy adults found a significant reduction in stress in the volunteers taking 600 mg. A number of possible active components of the dried leaf and essential oil of the herb may be responsible for these effects, such as eugenol and citronellol, which bind to GABA-A receptors and increase the affinity of GABA to receptors.

ANTIVIRAL

A lemon balm extract was found to have significant virucidal effects against HSV-1 within 3 and 6 hours of treatment in vitro and in animal tests. The volatile oils from Melissa officinalis have also been shown to inhibit the replication of HSV-2 in vitro.

ANTIBACTERIAL AND ANTIFUNGAL

One in vitro study found that lemon balm extract exhibited activity against bacteria, filamentous fungi and yeasts. It is likely that the constituent eugenol is chiefly responsible, as it has well established antibacterial activity against such organisms as Escherichia coli and Staphylococcus aureus.

CHOLINERGIC

Lemon balm exhibits CNS acetylcholine receptor activity, with both nicotinic and muscarinic binding properties. In vitro data has demonstrated that lemon balm is a weak inhibitor of acetylcholinesterase and has a moderate affinity to the GABA-A benzodiazepine receptor site. This indicates that lemon balm may have a role to play in the treatment of Alzheimer’s disease and epilepsy. However, a 2003 randomised, double-blind, placebo-controlled, crossover trial demonstrated that lemon balm did not inhibit cholinesterase. The trial demonstrated improved cognitive function and mood and concluded that for these reasons it was a valuable adjunct to Alzheimer’s therapy.

Clinical Note

Long before the current biologically based theory of cholinergic abnormalities in Alzheimer’s dementia emerged, western European medicine systems have traditionally used several herbs that are now known to exert cholinergic activity (such as sage and lemon balm) for their dementia-treating properties.

ANTI-INFLAMMATORY, ANALGESIC AND ANTISPASMODIC

The plant extract exerts analgesic activity at high doses in vivo. Two constituents in lemon balm have documented anti-inflammatory activity, achieved through different mechanisms of action. Rosmarinic acid, a naturally occurring constituent found in Melissa officinalis, inhibits several complement-dependent inflammatory processes. Eugenol, another important component, inhibits COX-1 and -2 activities in vitro. Both the whole volatile oil and its main component citral have demonstrated antispasmodic ability on isolated rat ileum.

ANTIOXIDANT

Lemon balm has shown antioxidant activity in several studies. According to a 2003 study, concentrations of antioxidants within lemon balm are >75 mmol/100 g.

CARDIOVASCULAR EFFECTS

Aqueous extracts of lemon balm have been shown to slow cardiac rate but not alter the force of contraction in isolated rat hearts. An extract of lemon balm reduced blood cholesterol and lipid levels in rats fed a high fat and alcohol diet. Interestingly, the extract also increased glutathione levels and reduced lipid peroxidation in the liver, demonstrating a hepatoprotective effect.

Lemon balm: Other Actions

In vitro testing has also identified anti-HIV activity with inhibitory activity against HIV-1 reverse transcriptase, inhibition of TSH binding to thyroid plasma membranes and the extrathyroidal enzymic T4-5′-deiodination to, and antitumour activity.