It contains chlorine dioxide - a bleaching agent.

Sather and others promoted the substance even before the coronavirus outbreak, and in January he tweeted that, "not only is chlorine dioxide (aka MMS) an effective cancer cell killer, it can wipe out coronavirus too".

Last year, the US Food and Drug Administration (FDA) warned about the dangers to health of drinking MMS. Health authorities in other countries have also issued alerts about it.

The FDA says it "is not aware of any research showing that these products are safe or effective for treating any illness". It warns that drinking them can cause nausea, vomiting, diarrhoea and symptoms of severe dehydration.