Fifty-three percent of pharmacists recommend Delsym as their top cough suppressant, according to U.S. News & World Report. Mucinex and Robitussin tied among the pharmacists, each gaining 21 percent of the votes. Vicks NyQuil only garnered 1 percent of the pharmacists' votes.
The active ingredient of Delsym is dextromethorphan, notes Drugs.com. Delsym suppresses a cough for up to 12 hours and should not be taken simultaneously with MAO inhibitors. Mucinex also contains dextromethorphan as its main cough-suppressing ingredient, and some versions of the drug also include the expectorant guaifenesin, which loosens mucus in throat and chest, making it easier to cough out congestion.