MMS, which forms chlorine dioxide when 'activated' with a substance like citric acid, is a very effective pathogen-killer - on that, scientists and proponents agree.

"Chlorine dioxide is used to treat drinking water precisely because it's so reactive - it kills bacteria and other microbes in water," University of Waikato senior lecturer of biological sciences Dr Alison Campbell told Newshub.

It's been linked to at least two deaths - one who was trying to ward off malaria whilst holidaying in the Pacific in 2010, and another who died of a perforated intestine in 2013. Dozens more have reportedly laid complaints to the US Federal Drug Administration about the substance.

MMS is distributed by "non-religious church" Genesis II. New Zealand representative Roger Blake told Newshub if chlorine dioxide works in water, there's no reason why it shouldn't also work in humans - after all, we're 70 percent water.

"What we're doing is nothing airy-fairy, snake oil," he said, going on to claim the side-effects some have reported - vomiting, nausea and rashes - only happen when people don't follow the instructions.

"If someone has disease in the body and you kill that disease too rapidly, you've got all this dead virus, bacteria material floating around the bloodstream which can't be filtered out by either the liver or kidneys by the rate that you've killed it, of course you're going to get a toxic overload. You're going to feel rotten."

He said there are no studies proving chlorine dioxide is bad for you. Dr Campbell said that's because it would be "rather unethical" to ask people to drink industrial-strength bleach.

"There are certainly animal tests that show it's harmful when taken internally," she said.