The recommended dosage for adults and children over 12 is 30 milliliters every six hours for liquid Nyquil and two capsules with water every six hours for NyQuil LiquiCaps, according to Vicks.com. Intake of either medication should not exceed four doses in a 24-hour period.
Patients should use a measuring device rather than a household spoon to ensure proper measurements, says WebMD. Patients should take NyQuil with plenty of fluids, unless a doctor directs otherwise.
NyQuil contains dextromethorphan to alleviate coughing, acetaminophen to relieve pain and reduce fever, antihistamines to reduce sneezing and irritation to eyes, nose and throat, and decongestants to reduce ear and nose congestion, according to WebMD. It is appropriate for treatment of temporary symptoms but not symptoms of ongoing health problems.