In a report completed three years ago, the Pentagon found that Rear Adm. Ronny L. Jackson had mistreated subordinates while serving as the White House physician and drank and took sleeping pills on the job. The report recommended that he face discipline.

Now it turns out that the Navy quietly punished him the next year. Though he had retired from the military in 2019, he was demoted to captain — a sanction that he has not publicly acknowledged.

Mr. Jackson, now a Republican congressman from Texas and an outspoken ally of former President Donald J. Trump, whose care he supervised in the White House, still refers to himself as a retired U.S. Navy rear admiral on his congressional website.

According to a former defense official and a current military official, Mr. Jackson was demoted from rear admiral to captain in the summer of 2022. The officials spoke on the condition of anonymity to discuss personnel matters. Mr. Jackson could not be reached for comment. His lawyer, Stanley Woodward, declined to comment.

In a statement on Thursday, a Navy official said only that the findings led the Navy to take administrative actions against him. The official would not say what those actions were.

The findings of the internal investigation suggest that Mr. Jackson’s behavior was “not in keeping with the standards the Navy requires of its leaders,” the Navy said in a statement on Thursday. “And, as such, the secretary of the Navy took administrative action in July 2022.”

A demotion of this type, even after retirement, is a significant blow in military circles, especially for someone who had been entrusted to be a physician to both Mr. Trump and President Barack Obama.

Mr. Jackson’s demotion was reported earlier by The Washington Post.

The demotion reduces his annual retirement pay by about 13 percent, according to military pay scales.

Mr. Jackson is a staunch supporter of Mr. Trump. When the former president was indicted in New York last year for his role in paying hush money to a porn star, Mr. Jackson lashed out at Democrats on social media.

“These cowardly Democrats HATE Trump and HATE his voters even more,” he wrote. “When Trump wins, THESE PEOPLE WILL PAY!!”

In his 2022 memoir, “Holding the Line,” Mr. Jackson referred to himself as a “Trump person” and noted that he had stood by the president after the Jan. 6 attack on the Capitol.

In early 2018, while serving as the White House physician, he delivered a public assessment that Mr. Trump, then 71, was in excellent health, without providing any supporting details like his cholesterol levels or blood pressure.

About two months later, Mr. Trump nominated Mr. Jackson to be the secretary of veterans affairs. But Mr. Jackson withdrew after reports began to emerge about his misconduct in the White House, including that he kept sloppy records and bullied his staff. After Mr. Jackson left the White House and the Navy, Mr. Trump backed his successful bid for Congress in 2020.

Mr. Jackson has called the Pentagon’s internal investigation into him a political hit job. In his memoir, he said the findings were shared with him a day after President Biden’s inauguration.

“If I had retired and not gotten into politics, this investigation would have never gone anywhere,” he wrote. “We’ll have to wait to see how this all plays out.”

His book was released on July 26, 2022. If he was aware of his demotion at the time, he did not mention it in his memoir.