Most cases of muscle cramps never get reported to public health authorities, so it’s difficult to say how common they are. But you probably know someone who’s had them. You’ve probably had them, too. And the older you get, the more likely you’re having one right now. Until not very long ago, quinine — a bitter-tasting substance sometimes associated with tonic water that was once the world’s mainstay treatment for malaria — was also the drug of choice for treatment of muscle cramps. But in 2006, the Food and Drug Administration warned against the use of quinine for this purpose, not because it was utterly ineffective but because of accumulating anecdotal evidence of adverse effects.