Hawthorn (Crataegus oxyacantha) - more accurately, hawthorn berry - is an herbal remedy from a shrubby tree native to Europe, North America and northern Asia. It has a long history of use to treat hypertension, atherosclerosis, congestive heart failure, and heart arrhythmias and was included in the U.S. Pharmacopeia until the 1930s.
The red berries of hawthorn contain phytonutrients called anthocyanidins and proanthocyanidins, antioxidants that strengthen the walls of blood vessels. Extracts of hawthorn berries, leaves and blossoms also contain compounds that have a tonic effect on the heart and vascular system. Products available in the United States include hawthorn leaves, flowers and berries, sometimes in combination. Look for products standardized to at least 1.8% vitexin, also known as vitexin-2"-rhamnoside, the primary active ingredient in hawthorn.
You can safely take hawthorn berry extracts indefinitely. My colleague Tieraona Low Dog, M.D., an internationally recognized expert in the fields of integrative medicine, dietary supplements and women's health, confirms that toxicity is quite low, and no adverse effects are known with long-term use.
Overall, however, hawthorn berry preparations haven't been as well studied as those of hawthorn leaf and flower. As a matter of fact, although hawthorn berry has been shown to be an effective treatment for angina (chest pain that can occur when blood cannot freely pass through narrowed coronary arteries) Germany's Commission E no longer recognizes its use. That commission now approves only preparations of hawthorn leaf with flower.
Very little research in the United States has been done on hawthorn berry using modern methods. If hawthorn is working for you, use a supplement that contains the leaves and flowers as well. While there is probably no harm in taking it, I wouldn't rely on hawthorn berry extract alone for treatment of any heart-related problems.
Andrew Weil, M.D.