President Trump slurred his words during a speech last month because a dose of cold medicine dried out his mouth, the president's physician told reporters at the White House on Tuesday.

Dr. Ronny Jackson, the doctor who performed Trump's official physical on Friday, addressed questions about why the president had appeared to slur his speech last month, likely referring to remarks Trump gave in early December announcing the administration's decision to recognize Jerusalem as the capital of Israel.

Jackson said he had recently given Trump a dose of Sudafed, which he said likely dried Trump's mouth ahead of the speech.

The doctor said Trump does not wear dentures, which was one theory circulated at the time for why Trump seemed to struggle with his speech that day.

Jackson fielded questions about the president's mental fitness for office amid speculation about whether Trump remains able to fulfill his duties. The president's physician said Trump is "mentally very sharp."

"Absolutely, he's fit for duty," Jackson added.