Some of New Zealanders' favorite natural health products have been branded as ineffective by Kiwi doctors.
In the latest New Zealand Medical Journal Digest, doctors Shaun Holt and Sarah Jeffries and health psychologist Andrew Gilbey claimed colloidal silver, deer velvet, arnica and rescue remedy are a "waste of time and money" and sometimes harmful.
Holt told The Press that of the "hundreds" of therapies and products, about 95 per cent were either not biologically plausible or not supported by research evidence.
Popular but ineffective products and therapies included deer velvet, rescue remedy, arnica, propolis, magnets, shark cartilage, the lemon detox diet, and megadoses of vitamin C to treat cancer.
Some products, such as colloidal silver, which is marketed as being beneficial for the immune system and in fighting diseases such as cancer, HIV and pneumonia, could be dangerous, he said.
"Silver does have some anti-microbial actions, but not only is there no clinical evidence of an efficacy for these serious indications, products have been shown to contain widely variable amounts of silver and can cause argyria - dangerous and untreatable silver poisoning," Stuff.co.nz quoted him as saying.
"The difficulty for people is, which are the 5 per cent of products and therapies worth trying? Use the ones with evidence behind them.
"The problem is people go on the internet, which is not reliable," he sated.
People often assumed a product or therapy worked because reputable people endorsed it in advertisements, he said.
"There is no reason deer velvet would work for anything, though it might produce a placebo effect. It's quite shocking how little research there is, and it's a reasonably big industry," Holt said.
Gilbey said people were paying big money for products and therapies that did nothing.
"I think people would be quite surprised. It would be lovely if you could get something out of the garden, or scrape something off a tree, and it will fight off cancer, but there are not many of those things around," he said.