FDA's chief scientist Dr. Stephen Ostroff will fill the top spot until the government names Hamburg's successor. Reuters

Dr. Margaret Hamburg, commissioner of the U.S. Food and Drug Administration (FDA), has decided to step down from her position, a report said Thursday, adding that the White House is expected to announce Hamburg’s resignation on Friday.

Hamburg, one of the longest-serving FDA commissioners, supervised various public health initiatives such as tobacco control, food safety and drug approvals since she took office in May 2009. While the government is yet to decide on Hamburg’s replacement, Dr. Stephen Ostroff, the FDA's chief scientist, will fill the top spot until a new commissioner is named after congressional approval, Reuters reported, citing a person familiar with the matter. Hamburg was named among the world's most powerful women by Forbes last year.

Hamburg’s resignation, according to the Wall Street Journal, does not come as a surprise, given that she recently picked Dr. Robert Califf, a prominent cardiologist and researcher from Duke University, as FDA’s deputy commissioner for medical products and tobacco policy. Many view Califf as Hamburg’s potential successor.

According to the Journal, Califf is said to be someone who is interested in the top job at the FDA. He was even considered for the position when Hamburg was selected as commissioner.

During Hamburg’s tenure, the FDA proposed to improve nutrition by limiting trans-fats in food while also requiring restaurants to mention calorie counts on their menus. The agency also introduced several measures to accelerate the development and review of new drugs, Reuters reported.

In 2011, FDA decided -- under Hamburg -- to allow an emergency contraceptive known as Plan B to be sold to teenagers. But, the decision was later overruled by the then Health and Human Services Secretary Kathleen Sebelius. However, the use of Plan B was eventually approved two years later.