A Sensodyne toothpaste ad has been banned for "misleading" consumers that it whitened teeth.
Watchdogs upheld a rival's complaint there was no evidence its True White product was any more effective than non whitening brands.
Makers GlaxoSmithKline (GSK) claimed the formulation was specially developed for people with sensitive teeth, and prevented and removed stains to restore the natural colour.
They said the toothpaste whitened through the chemical cleaning action of sodium tripolyphosphate (STP), rather than dental abrasives common in other whitening toothpastes.
But the Advertising Standards Authority said the ad, which appeared on Sensodyne's website, was misleading, unsubstantiated and exaggerated.
They said it "must not appear again in its current form."
They added: "We told GSK not to mislead consumers by implying Sensodyne True White was perceptibly more effective at whitening teeth than other Sensodyne non-whitening toothpastes, unless they held adequate evidence that it was."
The ad featured an image of the toothpaste alongside its outer packaging, with the brand name 'TRUE White' visible on both.
The headline stated 'Now you can have sensitive tooth care and whiter teeth*', with the asterisked qualification '*With twice daily brushing' underneath.
It said Sensodyne True White was ten times less abrasive than many everyday whitening toothpastes.
Rivals Colgate said the toothpaste's whitening effect was not greater than that of standard non-whitening products.
GSK submitted five randomised controlled clinical studies which they said showed it was, with two finding it had a similar effect to an everyday standard whitening toothpaste, and one saying it was better.
The ASA said consumers would infer the toothpaste was able to "whiten teeth to a perceptibly greater extent than ordinary Sensodyne toothpastes that were not marketed as whitening toothpastes would be able to."
They said: "One of the studies reported statistically significant greater stain removal for True White compared with the whitening and non-whitening standard toothpastes, but the other four studies reported no statistically significant difference."
They added: "In addition, none of the studies compared the toothpaste to a non-whitening Sensodyne toothpaste, meaning no evidence was provided to show this toothpaste was more effective at whitening than other Sensodyne toothpastes that were not marketed as whitening toothpastes.
"Because consumers were likely to understand from the ad that Sensodyne True White was particularly effective at whitening, when we had not seen evidence that it had a perceptibly greater whitening effect than Sensodyne non-whitening toothpastes, we concluded that the ad was misleading."