These are crystals of the antiarrhythmic drug, Quinidine, which was created to treat abnormal heart rhythms. Studies have shown that some antiarrhythmic drugs can increase the risk of death from heart malfunctions, and so the drug is used only to treat life-threatening arrythmias. Quinidine and its stereoisomer, quinine (the stuff that is found in tonic water) have been shown to ward off malaria in certain scenarios.