Paracelsus
Paracelsus was responsible for the creation of laudanum, an alcoholic herbal opium preparation. It was in common use up to the 19th century. Like most of the alchemists, he was a notable botanist. He wrote various books, but especially his major work (title translated as: On the miners' sickness and other diseases of miners). This listed the occupational hazards of metalworking, including treatment and prevention strategies. He also wrote a book on the human body which contradicted Galen's ideas. He disagreed with Galen's idea of four humours, and instead believed that disease could come from an external source.