A team from the New York University says that glycyrrhizic acid could stop the virus triggering a form of cancer called Kaposi sarcoma.
The disease causes tumours to develop in tissues below the surface of the skin and is often found in people with a depressed immune system.
Writing in the Journal of Clinical Investigation (115, pp642-652), the scientists showed that glycyrrhizic acid could kill cells that were harbouring the herpes virus associated with Kaposi sarcoma.
The compound was able to disrupt the action of the key genes that control the virus' ability to stay lurking in a cell, but with the potential to trigger disease.
The researchers say their work is the first time an anti-viral agent has been found that specifically targets genes required to maintain the virus in a latent state.
In an accompanying commentary, Dr Jeffrey Cohen, from the US National Institutes Of Health, said: "While a compound present in liquorice may seem like an unlikely candidate for the treatment of virus-associated cancers, it is important to remember that other traditional drugs have proved highly effective for some infectious diseases."
"Extracts of the wormwood plant, which is a traditional Chinese medication for treatment of febrile illnesses, contain artemisinin - derivatives of this compound have become first-line treatments for drug-resistant malaria."
Liquorice is used as an alternative remedy for gastric and duodenal ulcers, sore throat, bronchitis, cough, arthritis, adrenal insufficiency, and allergic diseases.
Glycyrrhizic acid derivatives have previously been shown to have anti-viral activity against SARS.