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Lemon balm: unpredictable effect on thyroid

; Ottawa Vol. 136, Iss. 7,  (Sep 2003): 24-25.

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Lemon balm (Melissa officinalis) is a perennial herb that belongs to the mint family (Lamiaceae).(1)(2) Its name comes from the leaf's lemony smell and taste. It was Europe's 'plant of the year' in the late 1980s.(3)

Why do people use it?

The E Commission, the group that determines official indications for herbal products in Germany, approved the use of lemon balm for nervous sleeping disorders and for functional gastrointestinal complaints, such as flatulence and abdominal bloating.(4)

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It is also used for rheumatism, indigestion, lack of appetite, as an antispasmodic, antimicrobial, antihormonal, and analgesic.(1)(2)(5)(6) Topically, lemon balm is used to shorten the duration of symptoms associated with cold sores (herpes simplex).

How does it work?

The pharmacologically active constituents are located in the leaves of the lemon balm shrub. Volatile oils, flavonoids, triterpenes, sesquiterpenes, caffeic acid, and rosmarinic acid have been isolated.(1)(2)(6)(7) The last two components seem to be responsible for several of the plant's pharmacological activities.

Rosmarinic acid has antioxidant and anti-inflammatory properties.(6) Caffeic acid has in vitro activity against tumour cell lines.

Unidentified components interfere with the production of T3 and T4 in the thyroid gland by preventing the binding of TSH on the gland receptors.(1)(2)(6) In Graves' disease, the same components prevent the binding of IgG to the TSH receptors. It can also bind to TSH directly, rendering it inactive. The essential oil, polyphenols, and tannins are responsible for the antimicrobial activity.

What is the evidence?

Clinical evidence is limited to a few trials on the topical use of lemon balm for cold sore and a trial evaluating its efficacy as an hypnotic agent. Two trials that included over 100 patients showed that a 1% topical preparation of lemon balm shortened the duration of symptoms associated with cold sores and decreased lesion...