Our experiments support the use of
lemon balm for treating Herpes simplex lesions and encourage clinical
trials on this medicinal plant.

Melissa officinalis L. (Lamiaceae) (lemon balm) is used in folk
medicine for nervous complaints, lower abdominal disorders and, more
recently, for treating Herpes simplex lesions. In this work the
antiviral activity of a hydroalcoholic extract of lemon balm leaves
against the Herpes simplex virus type 2 (HSV-2) was assessed by the
cytopathic effect inhibition assay on Vero cells (ATCC CCL-81), in
comparison with acyclovir. The cytotoxicity of the extract on Vero
cells was previously tested by evaluating the cellular death and was
confirmed by the Trypan blue test. Lemon balm showed to reduce the
cytopathic effect of HSV-2 on Vero cells, in the range of non-toxic
concentrations of 0.025-1 mg mL(-1) (with reference to the starting
crude herbal material). The maximum inhibiting effect (60%) was
obtained with 0.5 mg mL(-1). The viral binding assay showed that the
extract does not prevent the entry of HSV-2 in the cells, thus
suggesting a mechanism of action subsequent to the penetration of the
virus in the cell. The extract was also chemically characterised by NMR
and HPLC analysis; it showed to contain cinnamic acid-like compounds,
mainly rosmarinic acid (4.1% w/w).