Codeine (codeine phosphate) contains the active ingredient codeine and is used to reduce pain from headache, the flu and common cold. See here for more information and to order.
A: Mucinex contains the active ingredient guaifenesin, which is an expectorant that helps loosen phlegm and thin bronchial secretions. Mucinex does not have rapid heart rate as a possible side effect. There is a product called Mucinex-D that contains pseudoephedrine, and this ingredient can increase heart rate.
Drowsiness. Drowsiness has been reported by people with depression, pain, high blood pressure, multiple sclerosis, stress and anxiety. (latest reports from 70,027 Drowsiness patients). On Sep, 28, 2015: 4,780 people reported to have side effects when taking Mucinex. Among them, 144 people (3.01%) have Drowsiness.