Sometimes disillusionment creeps in one small letdown at a time. But for Britt Marie Hermes, the transition from alternative medicine practitioner to sceptic occurred over the course of a weekend.

After an unsettling discovery at the Arizona clinic where she worked four years ago, Hermes turned her back on everything she had believed in and set out to expose what she describes as the dubious and unethical underbelly of her former profession. Hermes’ blog, Naturopathic Diaries, has gained a huge following in the sceptic community. But it has also angered some proponents of alternative medicine: Hermes is being sued for defamation by an American naturopath called Colleen Huber, in a case that is due to be heard in a German court later this year. So enthusiastic is the sceptic community that within nine days an international fundraising campaign had raised $50,000 (£36,000) to cover Hermes’ legal fees.

So how did a former proponent of natural therapies come to take on America’s powerful alternative medicine establishment?

Naturopathy, Hermes explains, encompasses a wide variety of complementary therapies – homeopathy, herbal supplements, dietary restrictions, acupuncture and faith healing would all be included – and promotes an overarching philosophy of “nature knows best”.

After obtaining her undergraduate degree in psychology from San Diego State University in 2006, Hermes applied to a four-year post graduate programme in naturopathic medicine at Bastyr University, near Seattle. “It’s set up to look as much like medical school as possible. The school claims they teach basic science courses at a medical level for the first two years,” she says. “Except there’s no entrance exams required.”

While in the UK alternative therapies have only a narrow intersection with conventional medicine, in the US the boundary is sometimes blurred. Twenty-three states and US territories have licensing systems that permit the use of the title “naturopathic doctor”. The roughly 6,000 registered practitioners are allowed to perform some medical tests, make diagnoses and prescribe certain medicines, as well as offer complementary cures and dietary advice. Some health insurers also cover naturopathic care.

So, Hermes recalls, it did not seem exceptional that the clinic where she was working in 2014 was treating cancer patients with a herbal compound called Ukrain. Shipments of the drug, stored in glass ampules that were broken open and sucked up into syringes, regularly arrived at the clinic. Cancer patients would pay for treatment in cash. One Friday, however, the Ukrain shipment had failed to materialise. When patients began to get agitated, Hermes brought the matter to the attention of her boss. “He mentioned that he suspected the FDA [US Food and Drugs Administration] had confiscated the shipment,” she says. “I found that statement really bizarre and it prompted me to read up more about it.

“I discovered immediately that [Ukrain] was not FDA-approved,” she says, adding that the meaning of this was not immediately obvious, as most naturopathic cures are not FDA-approved. But then she realised that it was potentially a federal crime to administer such a drug to cancer patients. “Once I realised that, everything changed virtually overnight,” she says. She spent much of the weekend on the internet reading critiques of her own profession. “By Monday morning I had hired a lawyer and I quit the practice.”

Shortly after leaving, Hermes started a blog, detailing her own journey of re-evaluation and increasingly publishing take-downs of alternative remedies. However, she says she did not initially find kindred spirits among the sceptic community. “My impression was that it was a group of old, white, grumpy men,” she said. She recalls reading words like “quack” and “fraudster” and finding these descriptions hard to reconcile with the people she had known in the sector.

In Britt’s experience, people typically turn to alternative therapies after a negative experience with a doctor or when conventional treatments have little to offer. As a teenager, she herself had encountered an unsympathetic doctor (“a jerk”) while seeking treatment for psoriasis. “I started taking dietary supplements in addition to the steroid cream,” she says. “I really felt that it was the supplements that were making my skin better and developed this narrative that natural is better.”

Later, naturopathy seemed a logical career choice. “It was definitely the emotional experience with alternative practitioners that really spoke to me,” she says. “I really wanted to offer that hope and kindness and empathy to patients of my own.” Her PhD project, at Kiel University’s department for evolutionary genomics, focuses on the skin microbiome in the context of inflammatory skin diseases.

Providing emotional support, she argues, is the one aspect in which mainstream medicine might learn something from alternative therapists. “They spend a lot of time with patients. They talk about emotional wellness and the details of how you’re sleeping and the quality of your sleep, so you form these close connections,” she says. “That can be really therapeutic.”

Hermes says the potential shortcomings of conventional medicine are seldom acknowledged as a motivation for people to seek out alternatives. And sceptics and the scientific community often focus only on debunking quack remedies rather than trying to understand why people seek alternatives in the first place.

Hermes thinks her poacher-turned-gamekeeper perspective explains the popularity of her writing, among both sceptics and people interested or working in naturopathy. “A lot of people like me – or like who I used to be – can look at my profile and sympathise,” she says. Her blog offers a mixture of personal insights (“It is surprisingly easy to sell snake-oil. I know, because I’ve done it.”) and warnings about the potential dangers of alternative therapies. “Don’t let a naturopath near your vagina,” warns a recent post about the dangers of a herb-based paste called “black salve” that has been promoted as a treatment for HPV infections.

The post that prompted Colleen Huber’s legal action focused on her clinic’s claims about its alternative treatments for cancer. Its website states: “85% of patients who completed our treatments and followed our food plan went into remission”. Huber is suing over comments on Hermes’ blog suggesting that she was misleading “vulnerable” cancer patients, and that her treatment was “fraudulent”.

In an email, the American Association of Naturopathic Physicians (AANP) states that for serious illnesses such as cancer, naturopathy can play a complementary role but should not replace conventional treatments. “Like all licensed medical providers, naturopathic doctors do not treat everything and are also trained to know when to refer,” a spokeswoman tells me. “They often work in collaboration with conventional healthcare providers or other specialists as determined by the patient’s condition and specific needs.”

There is evidence that alternative medicine is on the rise. According to the AANP, 38% of adults in the US are using some form of complementary or alternative medicine and last year three more states – Massachusetts, Pennsylvania and Rhode Island – introduced licensing systems for naturopathic practitioners. In the UK, surveys have found that around 40% of adults have used alternative therapies in the past year, with herbal medicine tending to be the most popular, followed by homeopathy, aromatherapy, massage and reflexology. Alternative cures are popularised by wellness and “clean eating” bloggers and celebrities including Gwyneth Paltrow.

Globally, one market analysis last year projected that the complementary medicine market would expand to have a revenue of nearly $200bn (£143bn) by 2025. “The alternative medicine industry in general seems to be on the rise in North America and I think in the UK as well,” says Hermes. “The political environment is ripe for that. There’s a feeling that experts aren’t necessarily the best people to trust, whether they are experts in medicine or in another field. When you have figureheads doubting the credibility of mainstream medicine, it creates a ripe breeding ground for the rise of pseudoscience.”

Most people who use alternative treatments, though, are capable of distinguishing between minor ailments and serious physical illness, which requires a doctor. If someone takes an arnica pill, is there really any harm in that?

“I’ve personally experienced the slippery slope,” says Hermes. “I went from cleaning out my diet, taking fairly harmless supplements, fish oils, to – over the course of 10 years – becoming totally immersed in naturopathy to the point where, had I been diagnosed with a serious illness I might have pursued natural therapies. So I take a pretty firm stance and say ‘no’ to all of it.”

• The standfirst of this article was altered on 10 April to correct a reference to “Britt Maria Hermes”.