A major component of clove taste is imparted by the chemical eugenol, eugenol comprises 72–90% of the essential oil extracted from cloves. The quantity of cloves required for culinary use is typically small; cloves pairs well with cinnamon, allspice, vanilla, red wine, basil, onion, citrus peel, star anise, and peppercorns.
In vitro (a medical study or experiment which is done in the laboratory within the confines of a test tube or laboratory dish), eugenol has shown to have following properties:
Antibacterial – tending to prevent the growth or spread of bacteria;
Antifungal – that limits or prevents the growth of yeasts and other fungal organisms;
Antioxidant – substance that protects cells from the damage caused by free radicals; and
Antineoplastic – acting to prevent, inhibit or halt the development of a neoplasm (a tumor).
Eugenol used in low doses may rarely result in side effects, while exposure or ingestion of a large amounts (as in overdose) can result in tissue injury and a syndrome of acute onset of seizures, coma and damage to the liver and kidneys.
(Sources of Information: ncbi.nlm.nih.gov and Wikipedia)