Joachim Dietrich Brandis (also Dietrich Joachim Friedrich Brandis) (born 18 March 1762 in Hildesheim, died 28 April 1846 in Copenhagen) was a German-Danish physician.
He was a son of the judge Christian Dietrich Brandis (1722–1800), and belonged to a prominent family from Hildesheim. He was the father of the philosopher Christian August Brandis and the grandfather of the forestry academic and administrator Sir Dietrich Brandis.
He studied medicine in Göttingen, earned a doctorate in 1785 and a Habilitation in Brunswick in 1791. In the following years he practised as a physician in the Duchy of Brunswick-Lüneburg. In 1803 he became Professor of Medicine at the University of Kiel, and in 1807 he founded a hospital in Kiel.
After saving the life of the wife of the Danish statesman Christian von Bernstorff, he earned great authority and respect at the Danish royal court, and moved permanently to Copenhagen in 1810. In Denmark he became personal physician to Queen Marie of Denmark and Norway, and he also lectured at the University of Copenhagen. He received the title Etatsraad (Councillor of State) in 1811 and the title Konferensraad (Privy Councillor) in 1828. He also became a member of the Royal Danish Academy of Sciences and Letters in 1819 and of the Royal Swedish Academy of Sciences in 1831.