US President Donald Trump has again defended the use of hydroxychloroquine to ward off coronavirus, contradicting his own public health officials.
He said the malaria medication was only rejected as a Covid-19 treatment because he had recommended its use.
His remarks come after Twitter banned his eldest son for posting a clip promoting hydroxychloroquine.
There is no evidence the drug can fight the virus, and regulators warn it may cause heart problems.
On Wednesday Dr Anthony Fauci, a leading member of the White House coronavirus task force, told the BBC that hydroxychloroquine was not effective against the virus.
"We know that every single good study - and by good study I mean randomised control study in which the data are firm and believable - has shown that hydroxychloroquine is not effective in the treatment of Covid-19," he said.
Last month, the US Food and Drug Administration (FDA) cautioned against using the drug to treat coronavirus patients, following reports of "serious heart rhythm problems" and other health issues.
The FDA also revoked its emergency-use authorisation for the drug to treat Covid-19. The World Health Organization (WHO) says "there is currently no proof" that it is effective as a treatment or prevents Covid-19.
In other developments:
- Coronavirus deaths in the US reached 149,250, according to Johns Hopkins University, as states in the south and west, including Florida and California, reported record daily death tolls. But Mr Trump claimed that large parts of the US were "corona-free"
- The US biotech company Moderna said its experimental coronavirus vaccine had induced a strong immune response in a study on monkeys. It said the vaccine protected against infection in the lungs and nose, and prevented lung disease
- Better known for making cameras, Kodak has moved into drug making and has just secured a $765m (£592m) loan from the US government. The fallen giant of the photography industry will make ingredients used in generic drugs to help fight the virus
What did Mr Trump say?
Studies commissioned by the WHO, the US National Institutes of Health and other researchers around the world have found no evidence that hydroxychloroquine - when used with or without the antibiotic azithromycin, as repeatedly recommended by President Trump - helps treat coronavirus.
Hydroxychloroquine was first touted by Mr Trump in March. Two months later he surprised journalists by saying he had begun taking the unproven medication to ward off the virus.
On Tuesday the president told reporters at the White House: "I can only say that from my standpoint, and based on a lot of reading and a lot of knowledge about it, I think it could have a very positive impact in the early stages.
"I don't think you lose anything by doing it, other than politically it doesn't seem too popular."
He added: "When I recommend something, they like to say 'don't use it'."
The comments were made as he prepared to visit Odessa, Texas for a fundraising event on Wednesday, despite concerns over surges of Covid-19 cases in the state.
Joe Biden, Mr Trump's presumptive rival in the November general election, criticised the trip. "Texas families are suffering. They're suffering because President Trump's inability to lead this country and combat the spread of Covid-19," Mr Biden said.
Why has hydroxychloroquine come up again?
President Trump and his son Donald Trump Jr were among social media users who shared video late on Monday of a group called America's Frontline Doctors advocating hydroxychloroquine as a Covid-19 treatment.
Facebook and Twitter removed the content, flagging it as misinformation, but not before more than 17 million people had seen one of the clips.
Twitter also banned the US president's eldest son from tweeting for 12 hours as a penalty for sharing the clip. In the past, Twitter has declined to remove tweets by President Trump himself and other world leaders, citing public interest and newsworthiness.
The video in question showed doctors speaking outside the US Supreme Court building at an event organised by Tea Party Patriots Action, a group that has helped fund a pro-Trump political action committee.
In the video, Dr Stella Immanuel, a doctor from Houston, says she has successfully treated 350 coronavirus patients "and counting" with hydroxychloroquine.
The president said on Tuesday: "I think they're very respected doctors. There was a woman who was spectacular in her statements about it."
According to the Daily Beast, Dr Immanuel has previously claimed the government is run by "reptilians" and that scientists are developing a vaccine to stop people being religious, among other bizarre views.
America's Frontline Doctors' founder Simone Gold accused social media companies of censorship for removing the hydroxychloroquine video.
"Treatment options for COVID-19 should be debated, and spoken about among our colleagues in the medical field," she tweeted. "They should never, however, be censored and silenced."
How is Mr Trump's relationship with Dr Fauci?
Late on Monday, Mr Trump also retweeted several tweets critical of Dr Fauci. But in Tuesday's briefing the president denied he was criticising the director of the National Institute of Allergy and Infectious Diseases, insisting: "I get along with him very well."
Asked about hydroxychloroquine earlier on Tuesday, Dr Fauci said the medication was not an appropriate treatment for Covid-19.
He told ABC News' morning show that the drug was "not effective in coronavirus disease".
The US now has more than 4.3 million reported cases of Covid-19, and more than 149,000 deaths.