http://www.nytimes.com/2008/08/05/health/05real.html?ex=1218600000&en=820377127aa89372&ei=5070&emc=eta1

THE FACTS

Leg cramps are especially jarring at night, when they can literally mean a rude awakening. They can strike suddenly, and they tend to become more common with age.

A popular remedy is quinine, which produces the bitter flavor in tonic water. But there are a couple of problems with that approach.

Quinine may be helpful. A large analysis in the journal BMJ combined data from several studies and found that people who regularly suffered nocturnal leg cramps experienced significantly fewer symptoms after taking quinine than did those who had a placebo.

But even if quinine prevents leg cramps, most types of tonic contain less than 1 percent of the amount found in a typical therapeutic dose.

Another problem, according to medical reports, is that in some people quinine causes allergic reactions, fever and even death. Since 2007, the Food and Drug Administration has recommended that it be prescribed only for the prevention and treatment of malaria.

Better to rely instead on stretching exercises to flex the legs before bedtime, according to the Mayo Clinic, which also recommends drinking plenty of fluids and eating foods high in potassium.

THE BOTTOM LINE

Some studies suggest quinine can ease leg cramps, but the side effects may outweigh any benefits.

ANAHAD O’CONNOR scitimes@nytimes.com