The BBC health series ‘Trust Me, I’m a Doctor’ teamed up with experts from University College London to test a selection of products bought from high street shops or online retailers.
Of 30 ginkgo products tested, eight contained little or no ginkgo extract.
In one case of milk thistle, unidentified substances were present in place of milk thistle.
All the evening primrose products performed well.
The UCL team tested around 70 products overall, using two methods – nuclear magnetic resonance spectroscopy and high performance thin layer chromatography – to study their composition.
Herbal products can be sold either as food supplements, or as Traditional Herbal Registration (THR) remedies.
In every THR tested, the product contained what was claimed on the label.
However, the food supplements showed a wide range of quality. Whilst many contained high amounts of the herbal ingredient as claimed, several had none at all.
The manufacture of THRs falls under regulation by the Medicines and Healthcare Products Regulatory Authority (MHRA), but herbal food supplements come under the remit of the Food Standards Agency (FSA) and Trading Standards at local authority level. Their manufacture is not regulated.