The company that manufactures Nurofen must pay a $6 million penalty it was handed for misleading consumers with its specific pain relief range, after a final appeal to the High Court was rejected on Wednesday.

The $6 million corporate penalty, the highest ever issued for misleading conduct under the Australian Consumer Law, was issued by the Full Federal Court in December last year.

The ACCC said the caplets in all four products contained the same active ingredient, ibuprofen lysine 342mg.

Following that decision, pharmaceutical company Reckitt Benckiser applied for special leave to appeal to the High Court of Australia on a number of grounds, including that the Full Court had erred in its assessment of consumer loss and in finding that the original penalty was manifestly inadequate.

The $6 million penalty was a revised figure, up from an initial penalty of $1.7 million, which was appealed by the Australian Competition and Consumer Commission for being an insufficient "deterrent" to a company of its size.