On Sept. 14, the FDA will ask a panel of outside experts whether dextromethorphan should be available only as a prescription. The agency is not required to follow the group's advice, though it often does. Mandating a prescription for the drug would deal a major blow to over-the-counter drug makers, which use the drug in dozens of combination cold medicines. Popular brands containing dextromethorphan include Wyeth's Dimetapp, Bayer's Alka Seltzer Flu Plus and Procter & Gamble's Vicks cough medicines. The drug is available in pills, gel caps, liquids and other forms.