Lemon balm (Melissa officinalis) is a perennial herb and common garden plant in Europe. Medically, it's used primarily to treat anxiety and insomnia. It acts as a mild sedative and may also help those whose stomachs are upset for emotional reasons. In Germany, the herb is approved for these purposes.
Lemon balm is also commonly used for pre-menstrual syndrome and to help with the symptoms of menopause. As well, it has antiviral properties. Test-tube studies show that it's active against herpes as well as HIV. Many practitioners suggest that a solution of lemon balm be applied to the skin when the symptoms of a herpes cold sore are first felt. Case reports suggest that this treatment is often quite effective.
Although there is less evidence on lemon balm in the treatment of HIV, people are including the herb in the combination of herbs they use to treat the virus. Lemon balm may decrease the activity of the thyroid, especially with long-term use. Naturopaths often suggest that people with underactive thyroids avoid this herb entirely.