Last reviewed by Editorial Team on September 5th, 2018.
NyQuil and Robitussin basic facts
NyQuil is a brand name for OTC medication which is used for relieving symptoms of common cold.
Product is a combination of 3 active substances: acetaminophen (usually in doses from 325mg to 600mg) used as a pain reliever and fever reducer, dextromethorphan (usually in doses of 15mg/pill or 30mg/30ml) used as a cough suppressant, it also has sedative properties and doxylamine succinate (usually in doses of 6.25mg/pill or 12.5mg/30ml) which is antihistamine with hypnotic effects that is used in combination with other drugs for relieving symptoms of cold and night-time allergy.
Some Nyquil’s preparations can contain other active substances such as: NyQuil D that contains nasal decongestive pseudoephedrine (30 mg/15 mL), NyQuil Sinus contains phenylephrine as nasal decongestant, Children’s NyQuil contains chlorpheniramine as antihistamine and has no alcohol.
NyQuil products on the market are: NyQuil Cold/Flu Multisymptom Relief, NyQuil D, Children’s NyQuil, NyQuil Cough, NyQuil Sinus and ZzzQuil.
Nyquil is available in syrup and and LiquiCap dosage forms. NyQuil contains sedating antihistamines, hypnotics, or alcohol, and that’s why it should be taken before sleep.
Robitussin is a brand name for OTC and prescription medications which are used for relieving cough and cold symptoms.
This Brand name is used for several cough syrup formulations that can contain different active ingredients: acetaminophen (pain reliever and fever reducer found in Robitussin CF), chlorpheniramine (antihistamine found in Robitussin children’s cough and cold syrups), phenylephrine (decongestant found in Robitussin CF and Daytime Cold + Flu), codeine (narcotic antitussive found in Robitussin DAC and Robitussin AC), dextromethorphan (non-narcotic antitussive found in most Robitussin products), diphenhydramine (antihistamine), doxylamine (sleep aid), guaifenesin (expectorant found in most Robitussin products), promethazine (antihistamine), pseudoephedrine (decongestant) and menthol (oral anesthetic in Robitussin DM lozenges).
Mechanisms of action – How NyQuil and Robitussin work in the body
Acetaminophen is highly selective COX-2 inhibitor that inhibits prostaglandin synthesis. It can inhibit COX-2 in CNS. Acetaminophen also acts on the hypothalamic heat regulating centers to produce antipyresis.
Dextromethorphan acts on cough center in medulla by decreasing sensitivity of cough receptors and by interrupting impulse transmission.
Doxylamine succinate is competitor for H1-receptor sites on target cells and also has anticholinergic effects, lowering labyrinthine function, blocking chemoreceptor trigger zone, and diminishing vestibular stimulation.
Pseudoephedrine and Phenylephrine are sympathomimetics with direct action on the adrenergic receptor system. The vasoconstriction is produced after α-adrenergic receptors activation.
Chlorpheniramine is antagonist of histamine H1 receptor (HRH1). It has been also shown that this drug is also a serotonin-norepinephrine reuptake inhibitor.
Guaifenesin acts by reducing the viscosity and increasing the volume of secretions in the trachea and bronchi. Studies have also shown that guaifenesin has muscle relaxant and anticonvulsant properties due to antagonism effects on NMDA receptors.
Can patients take NyQuil and Robitussin together
There should be no need to take those medications together at the same time as they act on the same way, so their effects will become additive and there is a high risk of serious side effects to happen.
NyQuil and Robitussin, both contain acetaminophen as an active ingredient, and these products are usually taken 3-4 times a day, so if these preparations are used at the same time, even in recommended daily doses, there is a high risk for acetaminophen to be overdosed (more than 4g daily), and this can cause potentially fatal, hepatic necrosis.
Some NyQuil and Robitussin products can contain pseudoephedrine and phenylephrine as active ingredients, and their potential interaction can amplify sympathetic (adrenergic) effects, including increased blood pressure and heart rate. Patients with cardiovascular diseases and patients with a history of heart attacks shouldn’t use these medicines.
NyQuil and Robitussins preparations usually contain antihistamines with hypnotic effects such as: doxylamine, diphenhydramine, promethazine or chlorpheniramine, so their combination may increase sedation and drowsiness.
A significant interaction that can cause cardiac arrhythmias or sudden death may occur after mixing NyQuil D that contains nasal decongestive pseudoephedrine and Robitussin formulations with antihistamine promethazine. However, this interaction is more likely to happen only in certain predisposed patients.
The table below shows the incidence of side effects after NyQuil and Robitussin administration in recommendable doses. This Incidence can be significantly increased if these drugs are taken together.
|Frequency Not Defined||Hypertension, Tachycardia, Hypotension, Reflex tachycardia, Severe peripheral and visceral vasoconstriction, Tremor, Dizziness, Excitability, Headache, Sedation, Sleepiness, Restlessness, Dermatologic rash, Increased appetite, Xerostomia, Anemia blood dyscrasias (neutropenia, pancytopenia, leukopenia), Bilirubin and alkaline phosphatase may increase, Urinary retention|
Special precautions and warnings during NyQuil and Robitussin administration:
- Patients shouldn’t use these medicines if they have used MAO inhibitors drugs such as furazolidone (Furoxone), phenelzine (Nardil), isocarboxazid (Marplan), selegiline (Eldepryl, Emsam, Zelapar), rasagiline (Azilect), or tranylcypromine (Parnate) in the last 14 days. Drug interactions can occur leading to serious side effects.
- Pregnant patients shouldn’t use these medications without medical advice; it is not known whether chlorpheniramine, pseudoephedrine or dextromethorphan will harm an unborn baby. Chlorpheniramine, dextromethorphan, and pseudoephedrine may pass into breast milk and may harm a nursing baby. These medicines should not be used if mother is breast-feeding a baby.
- Patients with phenylketonuria should avoid these medicines.
- Children younger than 4 years should also avoid these medicines. These medicines shouldn’t be taken for longer than 7 days in a row.
- These medications may impair your thinking or reactions and cause blurred vision. Patients should be careful if they drive or do anything that requires being alert and able to see clearly.
- Patients should avoid alcohol while using these medications. Drinking alcohol can increase certain side effects of these medications.
- Patients should avoid becoming dehydrated or overheated during exercises. Chlorpheniramine can decrease sweating and patients could become more prone to heat stroke
- Patients should avoid these medications if they also take caffeine pills, diet pills, or other stimulants. Taking decongestants (pseudoefedrine, phenylephrine) together with stimulants can increase the risk of unpleasant side effects.
- Medicines such as sedatives, sleeping pills, narcotic pain medicines, medicine for seizures, anxiety or depression, and muscle relaxers can add sedation and sleepiness that can be also caused by dextromethorphan, chlorpheniramine, promethazine, doxylamine and pseudoefedrine.
Informations retrieved from: