The name Crataegus Oxyacantha is derived from the Greek phrase kratos, interpreted as hardness (of wood), oxcus (sharp), and akantha (a thorn). Hawthorn is perhaps best known for its use in cardiovascular conditions. The folk history of this herb is profound, with applications for several conditions relating to the cardiovascular system. Older folk history regarded the hawthorn as sacred for some traditions; the ‘Crown of Thorns’ was made from this plant.  Among its most prominent historical uses include its inclusion in topical poultice for sores and ulcers, or as a wash for itching and frost bite. Other uses included indigestion, gas, diarrhea, and abdominal pain in general. Internally, it was used for tapeworm infections and dysentery, a bacterial infection of the intestines.  Other than its use as a medicinal herb today, hawthorn is made into jams, jelly, candied fruit, and even wine.
Several parts of hawthorn are used medicinally. The leaves, fruit, and flower all have varying levels of active constituents. The majority of the active constituents from hawthorn are known as flavonoids; these include vitexin, rutin, quercitin, and hyperoside. Others include a class known as oligomeric proanthocyanidins (OPCs); these compounds are responsible for the beneficial medicinal effects of other herbs such as bilberry and green tea, among others. OPCs are also found in red wine. Researchers believe that this OPC content may explain some of the benefits observed from drinking these types of wines.
Much of the existing research on hawthorn continues to validate its role in cardiovascular conditions. Hawthorn exerts its effects on the heart muscle by strengthening the force of the contraction and increasing the brief period of time between heartbeats; during which, the heart muscle has a chance to ‘rest’.  By exerting these effects, blood flow to the heart (coronary blood flow) is improved and cardiac output (the amount of blood pumped with each beat) in increased. Additionally, as these effects increase the efficiency of the heart muscle, requiring less oxygen for sustainment. Newer research has also defined a role for hawthorn in the use of irregular heartbeats, as it appears to have some antiarrhythmic activity. 
Modern research lends the most concrete evidence to using hawthorn for congestive heart failure (CHF). Subjects taking the herb for this condition were noted to have improved exercise tolerance (the ability to exercise without discomfort), improved heart function (as evidenced by increased ejection fraction), and decreased negative perceptions/symptoms associated with having CHF. [5, 6] Additionally, subjects with CHF who were on additional diuretic medicines experienced an improvement in exercise tolerance and a decrease in adverse CHF symptoms when taking hawthorn after roughly 3.5 months of treatment. 
The actions of hawthorn on the heart tissue make it suitable for use in conditions other than CHF as well. These may include; poor coronary blood flow, angina, and arrhythmias. In hypertension (high blood pressure) hawthorn is used to increase cardiac output, enhancing the efficiency of the heart. For the peripheral vascular system, hawthorn is employed for treatment of elevated blood lipids (lowers serum cholesterol, LDL, and triglyceride levels), Buerger’s disease, and atherosclerosis.
The active constituents in hawthorn are noted for their antioxidant activity as well.
Some recent research has investigated the use of hawthorn in conditions of anxiety, combined with the mineral magnesium and another sedative-type herb (California poppy).  Investigators found that this combination was more effective than placebo and had minimal side effects when treating mild to moderate anxiety conditions.
Several hawthorn preparations are standardized to contain a higher active constituent content of flavonoids and OPCs. When standardized, it is typical to contain 2.2% flavonoids and 18.75% OPCs. 
Hawthorn is typically dosed at 160 to 1800 milligrams total, administered in divided doses throughout the day.  Oftentimes, the effects of hawthorn take 1 to 2 months to become apparent.
Hawthorne Side Effects:
Hawthorn rarely causes side effects and is well tolerated as a medicine. However, some reports list vertigo and dizziness as possible side effects.  Other less often reported side effects include nausea, gastrointestinal discomfort, headaches, insomnia, and sweating.
Hawthorne General interactions (supplement, herb, food, lab):
Hawthorn will not interfere with any foods. The blood pressure lowering effects of hawthorn may enhance the effects of other herbs or supplements with similar effects. Use caution when combining multiple supplements and herbs with similar effects as a synergistic response may occur. Because hawthorn has cardiac boosting effects, it should also be used with caution with other cardiac-specific herbs.  Consult with a physician that is knowledgeable about natural medicines regarding these interactions.
Hawthorne Drug interactions:
Hawthorn’s cardiovascular effects may either cause additive medication effects (thereby disrupting prescribed dose regimens) or antagonize the effects of other prescription medicines. In general, beta-blockers, calcium channel blockers, digoxin, and nitrates should be used with exceptional caution and guidance when taking hawthorn as well.
Taking hawthorn with an additional drug class, i.e. phosphodiesterase-5 inhibitors, may lead to additive effects as well. Some of the most popular drugs existing within this classification include; Viagra, Cialis, and Levitra.
Hawthorne Disease conditions:
Use of hawthorn in cardiovascular conditions may either interfere or potentiate existing drug therapies used for treatments of these conditions.
1 Online document at: http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml
2 Online document at: http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml
3 Pittler MH, Schmidt K, Ernst E. Hawthorn extract for treating chronic heart failure: meta-analysis of randomized trials. Am J Med 2003;114:665-74.
4 Chang Q, Zuo Z, Harrison F, Chow MS. Hawthorn. J Clin Pharmacol 2002;42:605-12.
5 Schmidt U, Kuhn U, Ploch M, Hubner WD. Efficacy of the Hawthorne (Crataegus) Preparation LI 132 in 78 patients with chronic congestive heart failure defined as NYHA functional class II. Phytomedicine 1994;1:17-24.
6 Zapfe jun G. Clinical efficacy of crataegus extract WS 1442 in congestive heart failure NYHA class II. Phytomedicine 2001;8:262-6.
7 Tauchert M. Efficacy and safety of crataegus extract WS 1442 in comparison with placebo in patients with chronic stable New York Heart Association class-III heart failure. Am Heart J 2002;143:910-5.
8 Hanus M, Lafon J, Mathieu M. Double-blind, randomised, placebo-controlled study to evaluate the efficacy and safety of a fixed combination containing two plant extracts (Crataegus oxyacantha and Eschscholtzia californica) and magnesium in mild-to-moderate anxiety disorders. Curr Med Res Opin 2004;20:63-71. 4 Ibid.
9 Degenring FH, Suter A, Weber M, Saller R. A randomised double blind placebo controlled clinical trial of a standardised extract of fresh Crataegus berries (Crataegisan) in the treatment of patients with congestive heart failure NYHA II. Phytomedicine 2003;10:363-9. 3 Ibid
10 Upton R, ed. Hawthorn Leaf with Flower: Analytical, quality control, and therapeutic monograph. Santa Cruz, CA: American Herbal Pharmacopoeia 1999:1- 29.