Marwān ibn Ǧanāḥ, known in the Jewish tradition as Rabbi Jonah, is renowned for his works on Hebrew grammar and lexicography, which he composed in al-Andalus in the first half of the eleventh century. Less well known is a fundamental work he composed on the nomenclature of medicinal drugs, the Kitāb al-Talḫīṣ (Book of the Commentary). This text was deemed to be lost until a complete manuscript was discovered in Istanbul in the 1970s (MS Ayasofya 3603). The authors, who are currently preparing an edition of the Talḫīṣ, sketch the profound influence of Ibn Ǧanāḥ’s book on the Arabic literature on simple drugs. They also discuss a number of aspects of the contents of the Talḫīṣ, which provide insights into Ibn Ǧanāḥ’s skills as physician and Arabic philologist. Special attention is devoted to passages that contain data with cultural, social or economical implications.