For thousands of years aspirin has been humanity’s wonder drug. Extracts from the willow tree have been used for pain relief in folk medicine since the time of the ancient Greeks. By 1897 a synthetic derivative (acetyl salicylic acid) of the plant’s active ingredient (salicin) was created. This allowed aspirin to become the most widely used medicine in the world. In recent years its benefits as a blood-thinning drug have led to it being prescribed in low doses of around 50mg to reduce deaths from stroke and heart attack. There were also hints that aspirin may help prevent some cancers. But these were mostly based on observational studies, which can be misleading.