The dosage of Mucinex Fast-Max for adults and children over age 12 is 20 milliliters of liquid or two caplets every four hours, according to the Mucinex website. Children under the age of 12 should not take this medication.
Mucinex Fast-Max contains dextromethorphan, guaifenesin and phenylephrine, according to Drugs.com. Dextromethophan, a cough suppressant, has an impact on the brain signals that trigger the coughing reflex. The expectorant quaifenesin loosens chest congestion so that it can be expelled through coughing. Phenylephrine HCl is a decongestant that shrinks swollen blood vessels in the nose to relieve nasal congestion.
Mucinex Fast-Max treats coughs and congestion related to colds, flu and allergies, as Drugs.com explains. However, it is not effective for treating coughs due to asthma, smoking and emphysema.
This medication can cause blurry vision and impair thought processes, warns Drugs.com. Those taking the medication must use caution when driving or undertaking any activity that requires clear vision and thinking. Alcohol intensifies the effects of Mucinex Fast-Max.
The common side effects of Mucinex Fast-Max include dizziness, drowsiness, nervousness, irritability and insomnia, according to Drugs.com, and it may also cause diarrhea. The more serious side effects for which a patient should seek medical assistance include fever; heart arrhythmias; severe headache, dizziness or anxiety; dangerously high blood pressure; and mood changes. Emergency medical assistance is required for those who experience the symptoms of an allergic reaction, which include hives, breathing difficulties, and swelling of the face, throat, lips or tongue.