Drinking lemon juice daily proved as effective as prescription drug therapy to prevent the formation of kidney stones in 2 recent studies reported at the May 2006 meeting of the American Urological Association.  Researchers either prescribed standard medication or lemonade for chronic stone-formers. 

The amount of lemonade used in the studies was 1/2 cup of lemon juice in 2 liters of water, which was drunk throughout the day.

In the end, both the medication and lemonade groups had the same results--fewer stones and higher citrate levels in their urine.  While medication (potassium citrate) did elevate citric acid levels more than lemonade, both products elevated citric acid levels to therapeutic levels.  Lemons are very high in citric acid, a compound that dissolves and prevents the formation of calcium oxalate--the substance that most kidney stones are made out of.

Dr. Stephen Nakada, M.D., chairman of urology at the University of Wisconsin in Madison, said,"Over several years we have rigorously prescribed lemonade therapy to most of our stone-forming patients."

Link to article reporting the results 

Another recent study validating lemonade for kidney stones. 

Another, 10 year-old study on lemonade and kidney stones. 

Reference:  American Urological Association, annual meeting, Atlanta, May 20-25, 2006; abstracts 1038 and 1537. Marshall Stoller, MD, vice chairman of urology and medical director, urinary stone center, University of California, San Francisco. Steven Nakada, MD, chair and professor of urology, University of Wisconsin, Madison. David Kang, Duke University Comprehensive Kidney Stone Center.