Barbara O'Neill (born 28 July 1953) is an Australian alternative health care promoter who advertises unsupported health practices described as misinformation and a risk to health and safety by the New South Wales Health Care Complaints Commission. She does not have any recognised qualifications and did not finish nursing training. She has presented her claims at alternative medicine organisations, wellness retreats, and Seventh-day Adventist Churches. She is married to Michael O'Neill, the founder of the now-defunct Informed Medical Options Party, an anti-vaccination and anti-fluoride political group.

In 2019, the Health Care Complaints Commission in New South Wales ruled that she is prohibited from providing any health-related services following several complaints from the public and health professionals. An investigation found that she provided dangerous advice to vulnerable patients, such as telling those with cancer to forego prescribed chemotherapy for bicarbonate of soda, and to give infants unpasteurised goat's milk. The investigation found that she also did not have any qualifications in a health-related field, and that she failed to meet the expected standards of unregistered health professionals.

O'Neill has promoted herself as a naturopath, nutritionist, and health educator since at least 2004, despite lacking any relevant qualifications or training. She has rejected the claim that her claims are unsupported, but admitted to not being able to provide any evidence when asked by the Health Care Complaints Commission.

She ran the Misty Mountain Health Retreat near Kempsey with her husband, charging clients as much as A$2,450 per person for a one-week stay for one person, to A$8,800 for two people for two weeks. She also provided paid telephone consultations. According to O'Neill's website, she provided detox services claiming to aid recovery from heart disease, diabetes, hormonal imbalance, chronic fatigue, candida/fungus, drug addiction, cancer, heartburn, and obesity.

Videos of her presentations have been viewed more than 700,000 times despite the HCCC ban. As a member of the Seventh-day Adventist Church, she has also spoken at churches. She previously worked at health retreats in Australia before she was barred from doing so by the HCCC, but continues to conduct them in New Zealand and the United States. She has also published several books on health and nutrition which include dangerous claims and advice.

The month following the HCCC's decision, O'Neill was scheduled to conduct a wellness program in the United States at a cost of US$2,350 per person. O'Neill continues to deliver programs aimed at cancer patients in the United States as of July 2023 at a cost of almost US$6,000 per person. O'Neill also delivers services in the Cook Islands.

According to the HCCC investigation, O'Neill falsely claimed to be able to cure cancer and urged clients not to use chemotherapy.

O'Neill promoted the discredited claim that cancer is a fungus that can be treated with baking soda. She has also claimed, without evidence, that one doctor had cured 90% of his patients' cancer with baking soda injections. She also encouraged her clients to cure cancer by eating a low carbohydrate diet for six weeks.

In late 2019, it was revealed that a Cook Islands man with stage four cancer had died after following O'Neill's advice, having declined medical intervention and attempting to treat his disease with bicarbonate soda, lemon juice, and boiled water. Supporters of O'Neill claim that he had been in remission for two years before his death.

O'Neill discouraged immunisation, claiming that all vaccines are harmful and the cause of a range of conditions. In one of her YouTube videos, she stated that "children can be naturally vaccinated against tetanus by drinking plenty of water, going to bed early, not eating junk food and running around the hills".

O'Neill has campaigned against the No Jab, No Pay initiative where most parental tax benefits are contingent on up-to-date vaccinations. She is also associated with the Informed Medical Options Party, a known alternative medicine and anti-vaccination political group who has drawn significant criticism from medical associations and health professionals.

In several of her YouTube videos, O'Neill discourages the use of antibiotics, promoting the disproven claim that they cause cancer. She has told pregnant women it is unnecessary to take antibiotics for Strep B because "no baby has ever died from Strep B catching out of birth". However, the Royal Australian and New Zealand College of Obstetricians and Gynaecologists' statistics show that 14% of newborns who contract early-onset Strep B die, and that antibiotics can reduce this risk dramatically.

O'Neill has recommended that parents who are unable to breastfeed their infant use substitutes besides formula. These have included unpasteurised goat milk and a mix of almond milk and dates or bananas. Co-author of the National Health and Medical Research Council (NHMRC) infant feeding guidelines, Professor Jane Scott, has stated this advice is "definitely not safe," and that "there is a real danger here for infants as these will not support healthy growth and development".

When provided with the NHMRC infant feeding guidelines for health practitioners, which provides evidence-based recommendations, O'Neill said that she had never read them and that she would refuse to.

Between October 2018 and January 2019, the New South Wales Health Care Complaints Commission (HCCC) received several complaints from health practitioners and the general public about O'Neill's health advice. These included a complaint that the advice she provided regarding infant nutrition could cause death if followed, where she disclosed her directives were not based on any guidelines or evidence.

The Commission found that some of her recommendations were based on ideas espoused by Tullio Simoncini, a disgraced Italian former oncologist and alternative medicine advocate incarcerated for fraud and manslaughter following the death of one of his patients. Some of her guidance was based on the views of doctors who were sued by patients for not providing appropriate treatment. When the HCCC noted these facts to O'Neill, she stated that she still intended to use their advice.

The HCCC also found that O'Neill could not recognise and provide health advice within the limits of her training and experience, and had failed to maintain records of the health advice she provided as required by law. While O'Neill has claimed to have received diplomas in naturopathy, nutrition, and dietetics from two now defunct organisations, the HCCC found that she did not have any health-related qualifications.

O'Neill claimed that she was merely providing clients with information rather than health advice, and that she never claimed to be able to cure cancer.

The HCCC ultimately found the O'Neill's actions had breached five clauses of the Code of Conduct for Unregistered Health Practitioners and that she poses a risk to the health and safety of the general public.

On September 24, 2019, the HCCC indefinitely banned O'Neill from providing health services or education in any capacity, regardless of whether or not she accepted payment for doing so. This precludes her from giving lectures, public speaking or seeing clients.

A HCCC spokesperson said that O'Neill's activities were being monitored closely and the prohibition order applies across New South Wales, Victoria, Queensland and South Australia. He also stated, "In general, if the material is accessible in [those jurisdictions] online, then it is considered to be delivering a health service", and that "Presenting health education in any form or delivering health services, would be a breach of her prohibition order."

Following the decision, O'Neill launched an online petition calling for the HCCC to reverse its decision. Accompanying the petition, O'Neill comments that, “It looks a bit dark now, but the Great God of the Universe will not let His wonderful health truth to be eliminated, regardless of how men and women may try.” She has also claimed to the press that she is a victim of a Nazi-style propaganda campaign.

In late 2019, O’Neill and her husband's Misty Mountain Health Retreat came under investigation by the Australian Charities and Not-for-profits Commission for alleged breaches of Australian charity law. Under its health promotion charity status, the Retreat had received government grants and various tax concessions. In defending its status, the Retreat had claimed it had provided diet, exercise and health advice to Aboriginal and Torres Strait Islander peoples and people with chronic and terminal illnesses, and that it had previously been branded as "The Aboriginal Healing Centre".

Although the HCCC ruling prevented her from providing or promoting her services, O'Neill continued to advertise through her website and that of the Misty Mountain Health Retreat.

In October 2019, Cook Islands health secretary Josephine Herman expressed concern after learning O’Neill had been running health workshops in Rarotonga, and referred the matter to the chief medical officer for investigation. Herman raised concerns regarding O'Neill's suitability to be delivering health services, including the legal requirement of an annual practising certificate amongst other documentation.

• Statement of Decision on Mrs Barbara O'Neill Archived 12 October 2019 at the Wayback Machine from the Health Care Complaints Commission