While quinine is actually an anti-malaria drug, doctors have also used it for decades to treat muscle cramps, too. But back in 2006, the U.S. Food and Drug Administration (FDA) cautioned against the off-label use of it to treat muscle cramps, citing 665 reports of serious effects from it, including 93 deaths.

These serious effects can include quinine toxicity, a cluster of symptoms including tinnitus (ringing in your ears), dizziness, disorientation, nausea, and visual changes. Heart arrhythmias, a decrease in blood platelets that can cause clotting problems, low blood sugar, and severe allergic reaction can occur, too.

Still, doctors continue to prescribe it off-label to patients suffering from muscle cramps, the study authors say.

What’s more, it’s also possible you can get regular exposure to quinine through non-prescription sources, like bitter lemon or tonic waters, which are also commonly taken for cramps. The amount of quinine in these is low, though—you’d have to drink more than one liter a day to reach the 100 milligram minimum of quinine used in the study.

However, it’s not yet clear if even small amounts of regular consumption can be a risk. More research needs to be done to clarify.

In the meantime, if a muscle cramp hits, stretch it out. But instead of holding the stretch for time, hold it for breaths—push into the stretch for three to five seconds as you fully exhale, then ease off during the inhale, says exercise physiologist Andrew Buskard, C.S.C.S., who has researched cramps.