How Long After Taking Zyrtec Can I Take Dayquil (And Why)?

Exact Answer: 1 Second to 48 Hours

Prescription medicines, anti-histamines, and drugs should be looked for their active ingredients thoroughly for their possible hazardous & dangerous interactions, as well as side effects when ingested together. The interactions between these drugs can either cancel out each other effects or dangerously increase the level of effects.

In extreme situations, the consequence of combined drug intake can prove to be fatal. Is consuming Vicks DayQuil after taking Zyrtec safe? It depends. In this article, there is a discussion on the side effects, dangers, and hazards of Zyrtec & DayQuil interactions.

Whenever, there are allergic symptoms like itching, sneezing, hay fever, hives, runny nose, watery eyes, or any other symptoms, then antihistamine drugs are ingested. Zyrtec is one such drug that is used to cure allergic symptoms. There are two types of Zyrtec available, which are completely different from each other.

How Long After Taking Zyrtec Can I Take Dayquil

How Long After Taking Zyrtec Can I Take Dayquil? 

Zyrtec is a simple second-generation antihistamine drug known as cetirizine. Whereas, Zyrtec-D is a combination of cetirizine & a nasal decongestant. Zyrtec & Zyrtec-D both remain in the bloodstream for at least 24 hours in the human body. Though a formulation of Zyrtec-D is also available for 12 hours. Cetirizine is an over-the-counter antihistamine drug. It works by blocking the receptors that produce histamine.

Zyrtec & DayQuil can be consumed together. There are no interactions between these two drugs. Sometimes, doctors may even prescribe both these drugs based on an individual’s symptoms. It is still advised that one should not consume both these drugs together without a prescription.

If you are planning to take DayQuil & Zyrtec together, it is advised to not work or drive as Zyrtec causes drowsiness. Instead, one can opt for other antihistamine drugs like allergen that don’t cause drowsiness. You can consume DayQuil & Zyrtec together if they are prescribed by a doctor.

The same is not true for Zyrtec-D. Pseudoephedrine is a nasal decongestant present in Zyrtec-D. DayQuil contains a nasal decongestant (phenylephrine) too. Drugs or medicines having similar active ingredients should never be consumed together. In our case, both the drugs have a nasal decongestant in common. 

As long as Zyrtec-D remains in the bloodstream, one should not consume DayQuil. Safer side, one should consume DayQuil only after 48 hours of Zyrtec-D consumption, irrespective of the type of the formulation (12 hours or 24 hours).

Ingesting DayQuil After TakingTime
Zyrtec1 Second to 24 Hours
Zyrtec-D24 Hours to 48 Hours

Why Can I Take Dayquil So Long After Taking Zyrtec?

Zyrtec & DayQuil can be consumed together because they do not share any active ingredients. Instead, they both work in tandem to deal with their respective symptoms. There are no interactions between these two drugs. Safer side, they still should not be consumed together.

The same is not true about the Zyrtec-D drug. The common misconception arises as DayQuil doesn’t have an antihistamine. DayQuil & Zyrtec-D share a common active ingredient, a nasal decongestant. Nasal decongestants provide temporary relief from pain due to a stuffy or running nose. They shrink the blood vessels of the nose that cause the congestion.

When a high dose of nasal decongestant is ingested by an individual, then multiple side effects may occur in the human body. The most prominent side effects are palpitations, insomnia, and high blood pressure. In most cases, these effects may not result in extreme situations.

As Zyrtec-D travels through the bloodstream, DayQuil should not be consumed as long as Zyrtec-D is not eliminated from the bloodstream. Based on the formulations, Zyrtec-D may stay around 24 to 48 hours in the bloodstream. It may differ from individual to individual. 


Old age, heart ailments, and other issues may result in Zyrtec-D remaining in the bloodstream for longer durations. Alternatively, if an individual feels that Zyrtec-D isn’t working, it is still advised that they should not ingest DayQuil. There may be multiple factors that cause a delay in the working of Zyrtec-D. 


Zyrtec is an antihistamine drug used to fight allergic symptoms. Antihistamines work by blocking the histamine receptors. Zyrtec-D also contains a nasal decongestant. It is advised that one should not ingest DayQuil with Zyrtec-D as it also has the same active ingredient. One can ingest DayQuil with Zyrtec if prescribed by a doctor.

Safer side, it is advised that one should not ingest DayQuil after taking Zyrtec-D till it completely exits the body. Zyrtec or Zyrtec-D may stay in the human for 12 to 48 hours in the human body.


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