In ‘An Account of the Foxglove and Some of its Medical Uses,’ published in 1785, Sir William Withering cautioned readers that extracts from the plant foxglove, also called digitalis, was not a perfect drug. ‘Time will fix the real value upon this discovery,’ he wrote. Now, more than 200 years later, researchers have validated Withering’s warning with the discovery that patients with atrial fibrillation who are treated with the digitalis-derivative digoxin are more likely to die than similar patients who received different treatments.