Probably not. Tonic water contains quinine, a malaria drug that’s also sometimes prescribed off-label to relieve nighttime leg cramps. But the Food and Drug Administration has warned against that use. And you’d have to drink liters of tonic water daily for weeks to get the amount of quinine usually used for cramps. What’s more, large amounts can cause blood disorders and have been linked to arrhythmias. A better approach if you get a leg cramp is to stretch and massage the affected muscle until the cramp goes away, usually within a few minutes.