Concocted of chlorine dioxide, a potent bleach used for stripping textiles and industrial water treatment, it is claimed to be an effective treatment against cancer, HIV, malaria and even Ebola.
It is sold in New Zealand through miraclemineral.co.nz as a "simple, scientifically proven pathogen killer".
One 125ml bottle of MMS, sold online as a water treatment, costs $26 plus $5 postage.
New Zealand's medical regulatory body, Medsafe, has followed the lead of the US Drug and Food Administration (FDA) and the UK Food Standards Authority in urging people to steer clear of MMS. "These products, when used as directed, produce an industrial bleach that can cause serious harm to health," Medsafe said.
Medsafe has instructed miraclemineral.co.nz to refrain from claiming its products are effective treatments for serious disease and not to sell MMS as medicine.
This weekend's seminar is being held at Ngatea Water Gardens Function Centre, owned by Roger Blake, who sells MMS.
Tickets were being advertised on the church's website for US$500 but Mr Blake said a simple donation would be accepted.
"They are not here to make money," said Mr Blake, a former mechanical engineer who has sold MMS to about 2000 customers, mostly in New Zealand.
"This seminar is not about introducing it to new people - basically everybody coming knows what it does, and has treated cancer for themselves. Most of them would've been dead without this product."
The Miracle Mineral Solution: made from bleaching agents used to whiten paper and water treatment. Photo / YouTube
He said: "It has treated everything from cancer, arthritis, hepatitis, shingles, chickenpox, and not one customer has complained."
More than 40 people have confirmed attendance for the seminar, which begins on Friday morning. It will feature talks by "Archbishop" Humble and other church members. Attendees will get lunch, booklets, a "Reverend ID card" and "Health minister ID card", and afterwards be authorised to "open a Church chapter".
The Australian Medical Association says 10 people have reported being poisoned by MMS in the past five years and has called for a ban.
The Victorian Poisons Information Centre told the Herald Sun newspaper it could cause "potentially life-threatening illnesses".
The FDA reissued a warning against the use of MMS this year after receiving "several reports of health injuries from consumers using this product, including severe nausea, vomiting, and life-threatening low blood pressure from dehydration".
In response, the church reposted a 2010 video that rejected the claims.
Mr Humble claims 5 million people have tried MMS worldwide over the past five years, with no major adverse effects.
Q & A
What is Miracle Mineral Solution (MMS)?
Sodium chlorite activates to form chlorine dioxide, a chemical compound commonly used as a disinfectant.
How does the church claim it works?
The Genesis II Church of Health and Healing says it is an effective destroyer of pathogens, fungi, disease, bacteria and viruses.
What does the church say it cures?
Cancer, HIV/Aids, Ebola, malaria, asthma, autism, hepatitis C, acne, flu.
Next trending article: Melbourne Cup horse Admire Rakti died from 'sudden death syndrome'
