Dr. Hahn, former chief medical executive of the University of Texas MD Anderson Cancer Center in Houston and a well-known radiation oncology expert, was nominated by President Trump. He succeeds Dr. Scott Gottlieb, who unexpectedly resigned on April 5, 2019. Dr. Ned Sharpless then temporarily became head of the FDA followed by Dr. Brett Giroir who took over on November 1, 2019.
Right at the beginning of his term in office, he will have to deal with a critical issue: the ban on flavoured e-cigarettes in the US. During his nomination phase, the US Senate already had many questions on this subject. However, there was no clear statement by Hahn. 

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CNN: Senate confirms Dr. Stephen Hahn as FDA commissioner