Officials in the Trump White House tried to pressure health experts to reauthorize a discredited Covid treatment, according to a congressional investigation.

A report published on Wednesday by the Democratic-led House select subcommittee on the coronavirus crisis contained new evidence of efforts to override Food and Drug Administration (FDA) decisions early in the pandemic.

The report also shed new light on the role TV personalities played in bringing hydroxychloroquine, an anti-malarial drug, to the attention of top White House officials.

The FDA authorized the use of hydroxychloroquine in late March 2020, based on small studies suggesting it could have some effectiveness against the coronavirus.

At that time, many researchers hoped existing antiviral drugs could be used. But by June 2020 FDA officials had concluded the drug was likely ineffective and could cause potentially dangerous heart complications. Authorization for emergency use was revoked.

The report by the House subcommittee focused on pressure on the FDA, which serves as gatekeeper for drugs, vaccines and other counter-measures against Covid.

The subcommittee chairman, James Clyburn of South Carolina, said: “As today’s report makes clear, senior Trump administration officials undermined public health experts because they believed doing so would benefit the former president politically.”

He also said officials had been “plotting covertly with known conspiracy theorists to dangerously push a disproven coronavirus treatment, bullying FDA to change its vaccine guidance, and advocating for federal investigations into those who stood in their way”.

Much of the subcommittee’s information came from an interview with Stephen Hahn, who Trump picked as FDA commissioner in late 2019. Frustrated by the pace of FDA reviews, Trump repeatedly accused Hahn – without evidence – of delaying decisions on Covid drugs and vaccines for political reasons.

Although FDA commissioners are politically appointed, agency scientists are expected to conduct reviews free from outside influence. Hahn told investigators he felt pressure due to the “persistence” of the Trump aide Peter Navarro to reauthorize hydroxychloroquine after the decision to pull its emergency use.

“We took a different stance at the FDA,” Hahn told investigators. “So that disagreement, which of course ultimately became somewhat public, was a source of pressure.”

Much of the report focuses on actions taken by Navarro and Steven Hatfill, a virologist and outside adviser described by the subcommittee as a “full-time volunteer” on Covid for the White House.

“Dr Hatfill and Mr Navarro devised multiple pressure schemes targeting FDA and federal officials who they contended were wrongly impeding widespread access to hydroxychloroquine,” the report said.

The report found that Hatfill and Navarro attempted to gain outside support for hydroxychloroquine by engaging “known extremists and prolific conspiracists like former White House chief strategist Steve Bannon, Jerome Corsi, and the Association of American Physicians and Surgeons” (AAPS).

The report found that Hatfill, under Navarro’s supervision, coordinated with the AAPS executive director, Jane Orient, and Bannon to gather support for a petition to “keep pressure on the FDA and the new emergency use authorization request”.

According to the report, Hatfill also “courted researchers to pursue a study to show the purported benefits of hydroxychloroquine by dangling millions of taxpayer dollars in promised funding – doing so after the drug was shown to be ineffective and potentially dangerous for certain patients”.

Responding, Hatfill said: “We never wrongly pressured anyone. We simply followed the science and the overwhelming evidence as detailed in several studies available at the time.”

Navarro said the subcommittee was “wrongly” claiming hydroxychloroquine to be “somehow dangerous”.

There is no evidence White House efforts changed FDA decisions on hydroxychloroquine or any other therapies.

In fall 2020, the focus of FDA and White House officials turned to the authorization of the first Covid vaccines, from Pfizer and Moderna.

As previously reported, the White House objected to an FDA requirement that vaccine makers gather two months of safety data before filing applications, contending it would delay launch of the shots. Trump repeatedly said shots would be authorized before election day, despite government scientists signaling that was unlikely.

The House report suggested that FDA guidance for vaccine manufacturers was delayed more than three weeks from mid-September until early October, due to White House concerns.

Hahn told investigators the agency faced “pushback about the issue” from officials including Trump’s chief of staff, Mark Meadows, who told Hahn on 23 September 2020 that the White House would not sign off on the two-month requirement.

On 6 October, the FDA published its vaccine guidelines as part of a larger set of documents for drugmakers. After the materials posted online, Hahn said Meadows called him to indicate that the guidelines were approved. The online publication drew fury from Trump on Twitter.

“New FDA rules make it more difficult for them to speed up vaccines for approval before election day,” Trump tweeted at Hahn. “Just another political hit job!”