Brazil's ex-health minister Nelson Teich told a Senate inquiry Wednesday he resigned over President Jair Bolsonaro's pressure to widely prescribe the drug chloroquine against Covid-19, despite evidence it was ineffective and potentially harmful.

Teich, the second of four health ministers who have served under the far-right president during the pandemic, resigned in May 2020 after less than a month on the job.

The 63-year-old oncologist has kept a low profile since, but was called to testify before a Senate commission investigating whether the government has been criminally negligent in its response to Covid-19, which has claimed nearly 412,000 lives in Brazil, second only to the United States.

Teich recalled his unease with Bolsonaro's pressure to recommend widespread use of the anti-malaria drugs chloroquine and hydroxychloroquine against Covid-19, which the president appeared to hope would provide a panacea and eliminate the need for lockdown measures.

"I realized I wasn't going to have the autonomy and freedom to lead that I thought were indispensable to do the job," Teich said.

"That lack of autonomy was most evident in my differences with the government on the effectiveness and extent to which the drug chloroquine should be used to treat Covid-19," he told senators.

Former Brazilian Health Minister Nelson Teich speaks during a session of the Parliamentary Inquiry Commission that will investigate the government's handling of the coronavirus pandemic in Brasilia on May 5, 2021
Former Brazilian Health Minister Nelson Teich speaks during a session of the Parliamentary Inquiry Commission that will investigate the government's handling of the coronavirus pandemic in Brasilia on May 5, 2021 AGENCIA SENADO / JEFFERSON RUDY

"My personal conviction, based on studies, was that there was no evidence for its effectiveness."

The politically explosive Senate probe could prove damaging for Bolsonaro as he gears up to seek re-election next year.

He faces backlash for downplaying Covid-19 as a "little flu" and attacking stay-at-home measures by local authorities, arguing they cause economic damage that is worse than the virus itself.

Like former US president Donald Trump, to whom he is often compared, Bolsonaro has fervently touted chloroquine against Covid-19.

However, numerous studies have found it ineffective against the coronavirus and raised concerns about side-effects, including heart and liver problems.

Teich was the second witness to testify before the Senate panel, following his predecessor, Luiz Henrique Mandetta.

Mandetta, who also resigned after clashing with Bolsonaro over Covid-19, told senators Tuesday the president had exacerbated the pandemic in Brazil and repeatedly ignored warnings that his policies risked causing the health system to collapse.