When looking into potential interactions between any drugs, it is important to consider all of the active ingredients involved.
This is especially true with combination ingredient products, like DayQuil, NyQuil and Zyrtec-D.
Unfortunately, as it concerns the three products in question (Zyrtec-D, NyQuil and DayQuil), they all share at least one drug in the same classification, and generally shouldn't be combined on a consistent basis.
In the next sections, I describe each interaction in detail. First, let's take a look at the active ingredients in each product.
Zyrtec-D Active Ingredients
Cetirizine is a 'second-generation' antihistamine, which are known for their long duration of action and their lack of sedative effects (when compared to first-generation antihistamines).
Pseudoephedrine is a nasal decongestant. It is also the active ingredient in 'Sudafed'. All pseudoephedrine products must be purchased behind the pharmacy counter after the passing of the Combat Methamphetamine Act of 2005.
Zyrtec-D is available in 12-hour and 24-hour formulations.
DayQuil Active Ingredients
Acetaminophen is an analgesic and the active ingredient in Tylenol.
Dextromethorphan is a cough suppressant.
Phenylephrine is a nasal decongestant, similar to pseudoephedrine. Unlike pseudoephedrine, phenylephrine products are available over the counter.
DayQuil also comes in a 'Severe' formula, which contains four active ingredients:
NyQuil Active Ingedients
NyQuil contains three active ingredients:
NyQuil contains the sedating antihistamine doxylamine. Doxylamine is a first-generation antihistamine, similar to Benadryl and is the ingredient responsible for making you drowsy.
Like DayQuil, NyQuil also comes in a 'Severe' formula:
Zyrtec-D With DayQuil
All DayQuil products (DayQuil and DayQuil Severe) contains phenylephrine, a nasal decongestant. Since Zyrtec-D also contains a decongestant (pseudoephedrine), they generally aren't recommended together.
Nasal decongestants, especially when more than one is taken, can increase blood pressure and the risk of cardiovascular complications (e.g. palpitations).
Additionally, high doses of nasal decongestants can cause nervousness and insomnia.
If you are looking to take DayQuil for symptomatic cold/flu relief, it would be recommended to take it with Zyrtec, not Zyrtec-D. Zyrtec only contains an antihistamine (cetirizine) and is safe to take with DayQuil.
SummaryZyrtec-D and DayQuil both contain nasal decongestants. Therefore, use together generally isn't recommended. You can however safely take Zyrtec (without the nasal decongestant) with DayQuil.
Zyrtec-D With NyQuil
NyQuil contains doxylamine, a sedating antihistamine.
Since Zyrtec contains cetirizine, another antihistamine, use together would be considered a therapeutic duplication.
As you would be taking two antihistamines if these products are combined, the risk of side effects increases. Side effects include:
- Excess sedation
- Dry mouth
- Dry eyes
Having said the above, your doctor may recommend taking NyQuil occasionally, only as needed, even if you are taking Zyrtec-D.
The risk of side effects is generally low and mild in severity. The benefit of an effective cold medication that acts as a sleep aid may outweigh the risks of combining two antihistamines on an intermittent basis. Just be sure to check with your doctor first.
You shouldn't, however, combine NyQuil Severe and Zyrtec-D in most situations.
NyQuil Severe contains phenylephrine while Zyrtec-D contains pseudoephedrine, two nasal decongestants. This interaction is described above in the 'DayQuil with Zyrtec-D' section (combining increases the risk of elevated blood pressure and other side effects).
SummaryZyrtec-D and NyQuil both contain antihistamines. Taking both increases the risk of side effects like sedation and dry eyes. NyQuil Severe and Zyrtec-D both contain nasal decongestants, which can increase blood pressure.
- Zyrtec.com Zyrtec Manufacturer Website.
- DEA CMEA (Combat Methamphetamine Epidemic Act of 2005).
- Vicks.com DayQuil Manufacturer Website.
- Vicks.com (Subscription Required) DayQuil Severe Manufacturer Website.
- NyQuil.com NyQuil Manufacturer Website.
- NyQuil.com NyQuil Severe Manufacturer Website.
- PubMed Effect of oral pseudoephedrine on blood pressure and heart rate: a meta-analysis.