The US Food and Drug Administration (FDA) has warned Procter & Gamble that its Vicks DayQuil Plus Vitamin C and Vicks Nyquil Plus Vitamin C are illegally marketed combinations of drug ingredients and a dietary ingredient.

The FDA informed the company that the over-the-counter (OTC) cold and flu medicines cannot be marketed because the ingredient combinations have not been proven to be safe and effective.

The agency previously determined that there was insufficient data to show that vitamin C is safe and effective in preventing or treating the common cold.

Under its OTC monograph system, the FDA does allow for some products to be marketed without agency approval, if they meet certain set requirements for labelling, formulations and indications.

According to the FDA, however, these two Vicks products do not comply with the applicable FDA monograph and must first be evaluated and approved under the FDA’s new drug approval process to be legally marketed.