From the ninth to the 13th century, numerous works on pharmacology were written in Arabic in Eastern as well as in Western parts of the Islamic world. Starting from Galen and Dioscorides, the Islamic authors greatly improved on the Greek heritage. Among the theories they developed, two major trends stand out. The first trend emphasized medicinal degrees of primary qualities, and thus could lead to the promotion of mathematical rules. The second trend, on the contrary, focused on ‘the whole form’ of the substances, and opened the way to an experimental approach. Both these trends will continue in European pharmacology up to the Modern period.