The advertising watchdog is investigating claims made by the makers of Nurofen after an Australian court ordered the company to step selling several versions of the popular painkiller.
Australia's federal court ruled that Reckitt Benckiser, the British firm which produces the over-the-counter drug, deceived consumers by selling Nurofen painkillers that were identical to its standard ibuprofen pills, but nearly twice as expensive.
The UK's Advertising Standards Authority (ASA) has now confirmed it is investigating 12 complaints about a television advert for Nurofen Express.
The watchdog is examining whether the advert was misleading because it implies that the product directly targets muscles in the head.
It is also looking into whether viewers were misled by the claim that the Nurofen Express "gives you faster headache relief than standard paracetamol or ibuprofen".
An ASA spokesman said: "We received the complaints in February and launched an investigation in March. This is a complex case and our investigation is ongoing.
"The advertiser is providing evidence to substantiate its claims, we're carefully assessing that and we'll publish our findings in due course."
Australia's consumer watchdog launched court action in March, arguing that consumers were being tricked into thinking that four products - Nurofen Back Pain, Nurofen Period Pain, Nurofen Migraine Pain and Nurofen Tension Headache - were designed to treat a specific type of pain, when in fact, they were all the same.
"None of the four products is any more or less effective than the others in treating any of the particular symptoms," Justice James Edelman wrote in his judgment.
A spokeswoman for Nurofen said the Australian court ruling did not affect its UK products and they would continue to be available.
Dr Aomesh Bhatt, the company's medical affairs director said: "The Nurofen specific-pain range was launched with an intention to help consumers navigate their pain relief options, particularly within the grocery environment where there is no healthcare professional to assist decision making."
A Nurofen spokeswoman refused to comment on the ASA investigation as it was "ongoing".
The UK's Medicines and Healthcare Regulatory Products Agency (MHRA) has no remit on medicine pricing and tends to intervene only when a product's name or description makes a medically misleading claim.
A spokeswoman said: "MHRA is responsible for ensuring the quality, safety, and efficacy of medicines including over-the-counter painkillers.
"For over-the-counter medicines informative names are permitted to help patients select an appropriate product without input from a healthcare professional."