All the profits from Duchy Originals goes to a charitable foundation
An advert for herbal remedies made by Prince Charles' Duchy Originals company was misleading, a watchdog has ruled.
An e-mail advert said they offered "alternative and natural ways of treating common ailments such as colds, low moods and digestive discomfort".
But the Advertising Standards Authority said it failed to state that the claims were not based on scientific evidence.
A Duchy Originals spokeswoman said "the breach was completely unintentional" and had been rectified.
The Duchy Originals organic and natural food brand was set up by Prince Charles in 1990 and all profits go to The Prince of Wales Charitable Foundation.
The e-mail promoted three "tinctures" - Echina-Relief, Hyperi-Lift and Detox - and was investigated by the ASA after a complaint from a member of the public.
It ruled the advert failed to carry the proviso, required by law, that their use was "exclusively based upon long-standing use as a traditional remedy" rather than scientific evidence.
That warning did appear on the products' packaging.
The ASA said the advert was misleading and must not appear again in its orignal form.
Duchy Originals said the company accepted the decision and had taken action.
"The breach was completely unintentional and, as soon as we were alerted to it, we changed the wording and put in place checks to ensure that all future wording is fully compliant with the code," a spokeswoman said.
The advert had already been deemed misleading by the Medicines and Healthcare products Regulatory Agency.
The body said it had given Duchy Originals a licence to sell the remedies, but did not enable it to make any claims about the effects of the remedies.
The Duchy Originals Detox Tincture also drew criticism from a leading scientist earlier this year.
Edzard Ernst, the UK's first professor of complementary medicine, said the product was based on "outright quackery" and accused Prince Charles of exploiting the public in times of hardship.
The Detox Tincture, which is an artichoke and dandelion mix, is described as "a food supplement to help eliminate toxins and aid digestion". It costs £10 for a 50ml bottle.