Can You Take Singulair (Montelukast) and Zyrtec Together Safely? Double-Therapy Rules
Written by: Dr. Muhammad Ihsan Ullah, PhD
Medically reviewed by: Dr. Asma Fareed Khan, PhD—Clinical Pharmacy
Last updated on September 19, 2026
When allergy symptoms remain troublesome despite treatment, combining medicines may seem like the logical next step. Singulair and Zyrtec are sometimes used together, but the decision requires more than checking whether the drugs interact. Their benefits, timing, side effects, and individual safety considerations all matter.
At a Glance
Singulair (montelukast) and Zyrtec (cetirizine) can generally be taken together because they target different allergy pathways and have no established direct interaction. No specific time gap is required. However, montelukast’s boxed warning and cetirizine-related drowsiness make individualised medical guidance and monitoring important.
Why Would a Doctor Prescribe Singulair and Zyrtec Together?
Cetirizine is a second-generation antihistamine. It blocks histamine H1 receptors, helping relieve sneezing, itching, runny nose, watery eyes, and hives.
Montelukast belongs to a different drug class called leukotriene receptor antagonists. It blocks the cysteinyl leukotriene receptor 1, or CysLT1 receptor, reducing leukotriene-mediated inflammation.
Because the medicines work through different pathways, a clinician may consider combination therapy when a single treatment does not provide adequate control. This is most relevant when allergic rhinitis occurs alongside asthma or when carefully selected patients remain symptomatic despite appropriate first-line treatment.
Why Would a Doctor Prescribe Singulair and Zyrtec Together?
Feature | Singulair (montelukast) | Zyrtec (cetirizine) |
Drug class | Leukotriene receptor antagonist | Second-generation antihistamine |
Main target | CysLT1 receptor | Histamine H1 receptor |
Common role | Asthma control; selected cases of allergic rhinitis | Allergic rhinitis and hives |
Availability in the United States | Prescription only | Over the counter |
Usual frequency | Once daily as prescribed | Once daily according to the label or clinician |
Important concern | Neuropsychiatric adverse effects | Drowsiness and reduced alertness |
Rescue treatment | No | No |
A 2026 network meta-analysis found that montelukast combined with certain second-generation antihistamines may improve some allergic-rhinitis outcomes compared with montelukast alone. Results varied across medicines and outcomes, however, and the authors reported substantial heterogeneity (1).
Do Singulair and Zyrtec Interact?
There is no established direct drug–drug interaction between montelukast and cetirizine. One drug is not known to prevent the other from working or routinely raise its concentration to a dangerous level.
Still, “no known interaction” is not the same as “safe for everyone.” Suitability depends on factors such as
- Age and reason for treatment
- Other prescription and nonprescription medicines
- Use of alcohol, cannabis, sedatives, or sleep medicines
- Kidney or liver impairment
- Pregnancy or breastfeeding
- Previous reactions to either drug
- A history of mood, behavioral, or sleep problems
Check product labels carefully. Zyrtec-D is not the same as regular Zyrtec: it contains cetirizine plus pseudoephedrine and carries additional precautions.
Can You Take Singulair and Zyrtec at the Same Time?
When both medicines have been recommended, they can generally be taken at the same time. There is no standard requirement to separate montelukast and cetirizine by a particular number of hours.
Taking them together may make the schedule easier to remember. Separating them is also reasonable when it improves adherence or helps manage cetirizine-related sleepiness. Do not take an additional dose because symptoms persist, and never double a dose after forgetting one unless a healthcare professional specifically instructs you to do so.
Should Singulair and Zyrtec Be Taken in the Morning or at Night?
Timing depends on the condition being treated and the way each medicine affects the individual.
Montelukast is generally taken once daily. When prescribed for asthma, it is commonly taken in the evening. For allergic rhinitis, timing may be individualized, but the medicine should be taken consistently according to the prescription.
Cetirizine is also commonly used once daily. Although it is less sedating than older antihistamines, it can still make some people sleepy. Evening administration may be more comfortable if drowsiness occurs.
Depending on professional advice, a practical schedule may involve:
- Taking both medicines in the evening
- Taking cetirizine in the morning and montelukast in the evening
- Taking montelukast in the morning and cetirizine at night when cetirizine causes sleepiness
The safest schedule is the one that follows the prescription, avoids duplicate doses, and does not impair daytime alertness.
What Side Effects Can Occur With Montelukast and Cetirizine?
The combination does not have a distinct, proven set of adverse effects. Instead, a person may experience effects associated with either medicine.
Cetirizine may cause:
Montelukast may cause headache or abdominal discomfort. More importantly, it has an FDA boxed warning for serious neuropsychiatric events. Reported changes include agitation, anxiety, aggressive behavior, abnormal dreams, insomnia, depression, and suicidal thoughts or behavior.
Stop montelukast and contact a healthcare professional promptly if new mood, behavioral, or sleep changes occur. Seek emergency assistance for suicidal thoughts, severe confusion, breathing difficulty, or swelling of the face, lips, tongue, or throat.
Alcohol and other sedating substances can worsen cetirizine-related drowsiness. Avoid driving or operating machinery until you know how the medicine affects you.
Is Montelukast Plus Cetirizine Better Than Cetirizine Alone?
Not necessarily. A randomized study found that combined montelukast and cetirizine reduced several seasonal allergic-rhinitis symptoms and was more effective than cetirizine alone for selected outcomes, including rhinorrhea and nasal or eye itching (2).
Broader evidence suggests that adding an oral antihistamine to montelukast may provide additional symptom relief in some patients, but improvement is not consistent across every symptom or study (3). Evidence of benefit must therefore be balanced against montelukast’s safety profile.
Clinical guidance recommends reserving montelukast for allergic rhinitis when alternative treatments have produced an inadequate response or cannot be tolerated (3). It should not be added automatically when mild symptoms could be managed with lower-risk options.
Can Montelukast and Cetirizine Be Taken Together Every Day?
Daily combination treatment may be appropriate when prescribed for a clear clinical reason. Continuing both medicines indefinitely without review is not advisable.
Periodic reassessment should determine:
- Whether both medicines remain necessary
- Whether symptoms have meaningfully improved
- Whether cetirizine is causing daytime sedation
- Whether mood, behaviour, or sleep has changed
- Whether another treatment offers a better risk–benefit balance
- Whether kidney function requires reconsideration of cetirizine use
Montelukast does not relieve an acute asthma attack and must not replace a prescribed rescue inhaler.
Can Children Take Montelukast and Cetirizine Together?
A clinician may prescribe both medicines to a child, but paediatric treatment must account for age, formulation, diagnosis, kidney function, and medical history. Adult doses should never be assumed to be suitable for children.
Parents and caregivers should use an accurate measuring device for liquids, avoid duplicate cetirizine-containing products, and monitor closely for mood, behavior, or sleep changes. A suspected double dose should be discussed promptly with the child’s clinician or Poison Control.
When Is Medical Advice Especially Important?
Consult a physician or pharmacist before using the combination if you:
- Are pregnant or breastfeeding
- Have kidney or liver disease
- Take sedatives or other allergy medicines
- Previously developed mood or behavioral changes with montelukast
- Are considering treatment for a young child
- Have worsening wheezing or uncontrolled asthma
- Remain symptomatic despite taking both medicines correctly
Medical Disclaimer
This content is intended for general educational purposes and does not replace individualized advice from a physician or pharmacist. Do not start, stop, or change montelukast or cetirizine without professional guidance. Seek immediate care for breathing difficulty, facial or throat swelling, suicidal thoughts, or another severe reaction.
Frequently Asked Questions
How Many Hours Apart Should Singulair and Zyrtec Be Taken?
No specific interval is generally required. They may be taken together or at different times according to the prescribed schedule and individual tolerability.
Can This Combination Make You Drowsy?
Cetirizine can cause drowsiness, although montelukast is not usually sedating. Avoid driving until you understand how treatment affects your alertness.
Can Zyrtec-D Be Used Instead of Regular Zyrtec?
Not automatically. Zyrtec-D also contains pseudoephedrine, which introduces additional risks and contraindications. Ask a healthcare professional before making the substitution.
What Should You Do After Accidentally Taking an Extra Dose?
Contact a pharmacist, clinician, or Poison Control for individualized instructions. Seek urgent care if marked sleepiness, confusion, breathing difficulty, or unusual behavior develops.
Should Montelukast Be Stopped if Mood or Sleep Changes Occur?
Stop taking montelukast and contact a healthcare professional promptly if new neuropsychiatric symptoms develop. Obtain emergency help for suicidal thoughts or dangerous behaviour.
References
- Wandana A, Tanely JC, Sudrajat RMC, et al. Evaluating montelukast–second-generation antihistamine combinations versus monotherapy in allergic rhinitis: a network meta-analysis. Asia Pacific Allergy. 2026;16(3):152–166. doi: 10.5415/apallergy.0000000000000236.
- Kurowski M, Kuna P, Górski P. Montelukast plus cetirizine in the prophylactic treatment of seasonal allergic rhinitis: influence on clinical symptoms and nasal allergic inflammation. Allergy. 2004;59(3):280–288. doi: 10.1046/j.1398-9995.2003.00416.x.
- Dykewicz MS, Wallace DV, Amrol DJ, et al. Rhinitis 2020: a practice parameter update. Journal of Allergy and Clinical Immunology. 2020;146(4):721–767. doi: 10.1016/j.jaci.2020.07.007.