Effects of Nyquil

NyQuil is the trade name for a line of over-the-counter products used to treat symptoms associated with colds and flu. Different NyQuil products have different ingredients with varying effects including fever reduction, pain relief, cough suppression, decongestion and sleep induction. All NyQuil products have more than one active ingredient; be sure to read the label to know what you are taking.

Fever Reduction and Mild Pain Relief

NyQuil D, NyQuil Liquid and NyQuil Liquicaps contain acetaminophen. This medication reduces fever and provides mild pain relief for the body aches associated with flu and flu-like viral illnesses. If you are taking one of these NyQuil products, be careful about taking other medications that may also contain acetaminophen. Do not exceed the total daily recommended dose of this or any other acetaminophen-containing product.

Cough Suppression

Children's NyQuil, NyQuil Cough, NyQuil Liquid, NyQuil Liquicaps and Nyquil D contain dextromethorphan, a cough suppressant. This medication acts on the cough center in the brain. Possible side effects of dextromethorphan include nausea, dizziness and sleepiness. People taking a monoamine oxidase inhibitor (MAOI) for depression should not take dextromethorphan because these drugs interact. Common MAOIs include phenelzine, tranylcypromine, selegiline and isocarboxazid. If you are taking an antidepressant and are not sure what type it is, talk with your doctor before taking NyQuil or any other medication to be sure it is safe for you.

Sleep Promotion

NyQuil Cough, NyQuil Liquid, NyQuil Liquicaps and NyQuil D contain doxylamine. This drug is an antihistamine, which can help you fall asleep. Many antihistamines including doxylamine cause drowsiness. Children's NyQuil contains chlorpheniramine, which is also an antihistamine. Like doxylamine, chlorpheniramine causes drowsiness and may help your child fall asleep. The antihistamine effects of both doxylamine and chlorpheniramine may help relieve sneezing and itchiness in the nose or throat.
People taking MAOIs or sodium oxybate should not take doxylamine because these drugs interact and may cause a dangerous reaction. Similarly, MAOIs and chlorpheniramine should not be taken together. Talk with your doctor if you have questions about prescription medications and what over-the-counter products to avoid.

Decongestion

NyQuil D contains the decongestant pseudoephedrine. Pseudoephedrine causes constriction of blood vessels, which reduces swelling in the nasal cavity and limits the production of nasal mucous. Pseudoephedrine can increase blood pressure. If you have high blood pressure, talk with your doctor before taking NyQuil D.
Although NyQuil D does not require a prescription, U.S. Food and Drug Administration regulations require that products containing pseudoephedrine be kept behind the pharmacy counter. You have to ask the pharmacist for NyQuil D; the amount you are allowed to purchase may be limited.