Sesquiterpene lactones, secondary metabolites of plants, present in a large number of species
mostly from the Asteracea family, are used in the traditional medicine of many countries for the
treatment of various pathological conditions. They exert a broad range of activities, including antiinflammatory,
anti-bacterial and anti-cancer properties. The best-known sesquiterpene lactones which
are already used as drugs or are used in clinical trials are artemisinin, thapsigargin and parthenolide.
Yet another sesquiterpene lactone, helenalin, an active component of Arnica montana, known for its
strong anti-inflammatory activity, has been used for centuries in folk medicine to treat minor injuries.
Unfortunately, helenalin’s ability to cause allergic reactions and its toxicity to healthy tissues prevented
so far the development of this sesquiterpene lactone as an anticancer or anti-inflammatory drug.
Recently, the new interest in the biological properties, as well as in the synthesis of helenalin analogs
has been observed. This review describes helenalin's major biological activities, molecular mechanisms
of action, its toxicity and potential for further research.