There is not sufficient evidence suggesting that tonic water, which contains quinine, is a safe, effective treatment for leg cramps, according to Consumer Reports. In fact, a report from the U.S. Food and Drug Administration states that serious complications could arise from using quinine to treat leg cramps.
Although the FDA has warned against treating leg cramps with quinine, an ingredient found in tonic water, doctors continue to prescribe this treatment despite the risks and effectiveness of the ingredient. Quinine is approved to treat malaria only, according to Consumer Reports and the FDA. Kidney failure and thrombocytopenia has been reported as side effects of using quinine to treat leg cramps.