A sales promotion on the website offered buyers facial injection treatments at a clinic in Bath.
Groupon said the promotion was for a voucher to be redeemed against a choice of dermal fillers and did not mention the possibility of using it for Botox, which is only available with a prescription.
However, the Advertising Standards Authority (ASA) found that the ad did refer to Botox and ruled that it must not appear again in its current form.
Last year the watchdog investigated and upheld 11 complaints against Groupon’s advertising.
The ASA said: “We noted their comment that whether or not the offer was for Botox, the promotion did not promote that particular aspect of the offer and was therefore not promoting a prescription-only medicine, although we disagreed.
“We considered that because the savings figures appear to have been calculated on the basis of Botox treatments, rather than dermal fillers, and in the absence of evidence to show that the promotion was for dermal fillers, we concluded that the promotion was for Botox, a prescription-only medicine.”
The advert, which was challenged by two complainants, related to Bath Facial Aesthetics.
In December last year the ASA referred complaints about Groupon to the Office of Fair Trading (OFT), stating that it had “serious concerns” about the company’s ability to adhere to the Advertising Code.
The ASA said in a statement that it was concerned by Groupon’s failure to conduct promotions fairly, such as not making clear significant terms and conditions, failure to provide evidence that offers were available, and exaggeration of savings claims.
A Groupon spokeswoman said: “Groupon takes any claims by the ASA very seriously.
“We have further improved our checks and processes around claims for health and beauty products to make sure our customers have the information they need to make informed buying decisions.”
She added: “In the case of administering any injectable treatments, we act in full compliance with all legal requirements.
“We only approve deals that are run by suitably qualified medical professionals or those acting under the instructions of qualified medical practitioners, in line with Medicines and Healthcare products Regulatory Agency guidance.”