Cranberry is a small plant, growing to a height of about 1 foot. It is an evergreen shrub that has dark green oval leaves, which produce the bright red berries we call Cranberries. The Cranberry is native to Eastern North America as well as Northern Asia. It is widely cultivated in the acidic boggy soils of New England in the US. 
Traditionally cranberry has been used as a culinary product, with its most well known use being the main constituent of cranberry sauces. It is also very popular as a juice, and has actually been consumed for centuries in this form, beginning back with the Swedish in the 1700’s. In the early 1800’s, cranberry began to be cultivated in massive quantities in Europe and subsequently, the United States.
Cranberry contains several different active constituents. It is very high in tannins, flavonoids, and Vitamin C. Most of its medicinal action is due to the high tannin content, particular the proanthocyanins. Proanthocyanins are also considered potent anti-oxidants. Other flavonoids that lend cranberry some of its medicinal action include the phenolic acids, which have been targeted for various applications concerning cancer cells. 
Medicinally, the berry (or fruit) part of the cranberry plant is commonly used. The other parts of the plant have not been thoroughly studied. Juice obtained from the berry can be used separately, as can the remaining pulp. Many of the supplements will either be in the form of powdered berry concentrate or a juice concentrate. 
The primary use of cranberry is as a preventative treatment for urinary tract infections (UTIs). Cranberry has been used for UTIs for decades. It has even been shown to prevent the adhesion of E.coli in study, the most common cause of bacterial infections in the urinary tract.  It is not an antibiotic, so it does not kill the bacteria once they have been established in the bladder. It merely makes the bladder wall “too slick” for the bacteria to adhere to. Subsequently, they are flushed out of the bladder in urine. Cranberry can be taken as a preventative measure in those who are susceptible to UTIs.
- Cranberry can also be used as part of a treatment regimen for acute urinary tract infections, though it will not kill the bacteria or decrease the duration of this condition. It may, however, provide a reduction in the severity of symptoms.
- Cranberry can also be used as a treatment for kidney stones. It is particularly effective against stones forming from calcium oxalate. It has been shown to reduce the risk factors that lead to this type of stone formation.  Cranberry may also reduce the risk factors associated with the condition known as “bladder gravel”. 
- Cranberry has shown several cardiovascular effects in animal models. It has been suggested that this fruit may be effective at decreasing the oxidation of LDL, or the bad cholesterol.  The oxidation of Low-Density Lipoproteins occurs primarily as a result of free radical damage. Cranberry is a potent antioxidant due to the high levels of flavonoids and tannins.
- Because of its high levels of flavonoids and antioxidant actions, cranberry may also be protective against the development of atherosclerosis.[ 7] Atherosclerosis is a major contributor to coronary artery disease and heart attacks.
- Cranberry is currently gaining acceptance as an anti-proliferative, or anti-tumor, agent. As previously mentioned, the high content of phenolic acids may be responsible for cranberry’s ability to inhibit many different cell lines of human cancers.  Flavonoids found in cranberry have also been shown to be effective against the spread of human cancer cells, including those of the breast, prostate, colon, lung, and brain, in vitro. 
The typical dosage of cranberry for urinary tract prevention and treatment is 300 - 400 milligrams, twice daily. This amount may be delivered via capsules, or 5 - 20 ounces of cranberry juice. Greatest results are obtained when cranberry products are standardized to 11 - 12% phenols. There are many different juice preparations on the market including juices sweetened with other fruits. However, the most effective form remains pure (straight) cranberry juice without any added ingredients. The more concentrated the juice, the more effective its therapeutic benefit.
Mild side effects from ingestion of cranberry include diarrhea and upset stomach. These symptoms completely resolve after discontinuance of the cranberry.
There is a potential for cranberry to interact with warfarin, a drug used for anti-coagulant therapy.  In one particular published case study, cranberry negated the effects of warfarin. If you are taking warfarin or any other anti-coagulant medication, it is imperative that you inform your physician before beginning any therapy with cranberry.
1. Chevallier A. Encyclopedia of Herbal Medicine, 2nd Ed. 2000. Dorling Kindersly, New York: 280.
2. Seeram NP, Adams LS, Hardy ML, Heber D. Total cranberry extract versus its phytochemical constituents: anti-proliferative and synergistic effects against human tumor cell lines. J Agric Food Chem. 2004 May 5; 52(9): 2512-2517.
3. http://www.pdrhealth.com/drug_info/nmdrugprofiles/herbaldrugs/101840.shtml Cranberry. January 2005.
4. Lynch DM. Cranberry for prevention of urinary tract infections. Am Fam Physician. 2004 Dec 1; 70(11): 2175-2177.
5. McHarg T, Rogers A, Charlton K. Influence of cranberry juice on the urinary risk factors for calcium oxalate kidney stone formation. BJU Int. 2003 Nov; 92(7): 765-768.
6. Wilson T, Porcari JP, Harbin D. Cranberry extract inhibits low-density lipoprotein oxidation. Life Sci. 1998; 62(24): PL381-386.
7. Reed J. Cranberry flavonoids, atherosclerosis, and cardiovascular health. Crit Rev Food Sci Nutr. 2002; 42(3Suppl): 301-316.
8. Ferguson PJ, Kurowska E, Freeman DJ, Chambers AF, Koropatrick DJ. A flavonoid fraction from cranberry extract inhibits proliferation of human tumor cancer cell lines. J Nutr. 2004 Jun; 134(6): 1529-1535.
9. Grant P. Warfarin and cranberry juice: an interaction? J Heart Valve Dis. 2004 Jan; 13(1): 25-26.