Experts have warned that clear information about possible side-effects is missing from some herbal remedies.
A study published in the journal BMC Medicine found that many products do not comply with new EU rules.
The rules insist herbal medicine should carry information about possible side-effects if taken with prescription medicine, but three quarters of the 68 products tested did not contain the warnings.
Professor of pharmacy, Theo Raynor, who led the study, said: "Consumers need reliable and comprehensive information when buying herbal medicines – information which tells them whether it is suitable for them."
Consumers have been urged to make sure any herbal treatments they purchase carry the THR logo, which proves they have traditional herbal registration.
"Those centres delivering herbal remedies should be registered and it should be compulsory for medicines distributed to have written information enclosed as a part of informed consent" - V Henry, London
"Herbal and other holistic remedies should have the same strict guidelines as any other product purchased. Lot numbers, expiry date, ingredients, side-effects, when to and not to use it etc" - Sandra Selby, Coventry
"More information should be given on what herbal medicines do and possible side-effects. Also information should be given regarding interaction with other medications and supplements" - Marilyn, Birmingham