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

Exact Answer: 7 – 8 Hours.

Zyrtec is an antihistamine that reduces the effects of the natural chemical histamine in the body. Histamine produces symptoms like sneezing, itching. watery eyes and runny nose. Zyrtec can be used in children and adults to treat allergy symptoms of sneezing and itching caused by histamine. It must be noted that taking additional medications along with Zyrtec can add to excessive sleepiness.

Nyquil, on the other hand, provides temporary relief from coughing, headaches, stuffy and runny nose, sore throat, fever and sneezing. It is extensively used by people with cold symptoms to sleep peacefully through the night.

Combining both Zyrtec and Nyquil may increase side effects such as increased dizziness, excessive drowsiness, confusion and difficulty in concentration. Thus, it is not recommended to take them both at the same time as both have the potential to cause sedation and may lead to additive side effects of both.

How Long After Zyrtec Can I Take Nyquil

How Long After Zyrtec Can You Take Nyquil?

It is highly advised by doctors not to take both medications one after the other immediately as Nyquil has an antihistamine in it and Zyrtec is also an antihistamine. Consuming both without a sufficient time gap in between will lead to an overdose of an excessive amount of antihistamine which is not the best way to treat cold or allergy symptoms.

It must also be noted that Zyrtec causes drowsiness more often in children, rather than in adults. After using Zyrtec, children might experience signs of cold diseases more than the usual side effects observed in adults. Thus, it is of vital importance not to consume both Zyrtec and Nyquil simultaneously.

Just because the majority of symptoms are similar for cold and allergy, it doesn’t imply that the medication for both can be taken together. The ingredients used in medications must be compared to avoid an overdose of a particular ingredient while taking multiple medications. That being said, one can safely take cold and allergy medication after some time when it is ensured that there will be no overlapping between their doses.

Zyrtec is a second-generation antihistamine that remains effective all day, whereas Nyquil contains doxylamine (sedating antihistamine) which is considered as first-generation since they are characterised by their relatively short duration of action and sedation which they cause.

Effectiveness Of Antihistamine In:Duration of action
ZyrtecAll Day i.e 24 Hours
Nyquil4 – 6 Hours

Why Does It Take So Long To Have Nyquil After Zyrtec?

Zyrtec and Nyquil must generally not be taken at the same time however, it is safe to take them both on the same day. Both must be separated from one another by at least a few hours to lessen the possibility of excess sedation and drowsiness.

The major concern with using both Zyrtec and Nyquil at the same time is due to the threats of potential additive side effects like drowsiness, dry mouth, dry eyes and excess sedation.

Zyrtec is used to treat allergic symptoms. It can be non-sedative if used during the day. Nyquil, on the other hand, is a cough suppressant used to treat symptoms of cold and flu. A decongestant Zyrtec works on the mechanisms of histamine reactions. It causes drying of the nasal secretions and thus, provides a sedating effect.

Both must not be taken together to prevent an overdose of sedation but certainly, both products satisfy their uses well when taken individually. Taking multiple medications together can cause liver damage and hence, the dosage of each of them must be taken strictly as prescribed by the doctor.

Even though Zyrtec should not be taken at the same time as Nyquil due to the possibility of additive side effects, one can take Zyrtec in the morning and if tolerated well enough, Nyquil can be taken in the night with no ill effects.


It is always better to use one medication at a time and not both at the same time. Taking multiple medications consisting of similar ingredients is not a good idea as it might lead to an overdose resulting in severe side effects.

Zyrtec is mostly used for treating various symptoms of allergies while Nyquil is mainly used for colds. While taking these medications, one has to be very careful about the side effects as both contain antihistamine which induces sedation.

When one is taking such medications on prescription, it must be thoroughly ensured that they are taken exactly as per the dosages mentioned and not more than that. If taken in prescribed doses there is no need for worrying and one is good to go.




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