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Nyquil vs. Flexeril: side effect and effectiveness comparison (a real world drug study)

Summary:

We compare the side effects and drug effectiveness of Nyquil and Flexeril. The phase IV clinical study is created by eHealthMe based on reports (from sources including the FDA) of 103,211 people who take Nyquil and Flexeril, and is updated regularly.

What is Nyquil?

Nyquil has active ingredients of acetaminophen / dextromethorphan / doxylamine / pseudoephedrine. It is often used in cold symptoms. eHealthMe is studying from 2,240 Nyquil users. Check the latest studies of Nyquil.

What is Flexeril?

Flexeril has active ingredients of cyclobenzaprine hydrochloride. It is often used in muscle spasms. eHealthMe is studying from 38,308 Flexeril users. Check the latest studies of Flexeril.

On Jul, 17, 2026

103,211 people who take Nyquil and Flexeril are studied.

Nyquil vs Flexeril drug comparison reports.

Drugs being compared in this study:

  • Nyquil (acetaminophen / dextromethorphan / doxylamine / pseudoephedrine)
  • Flexeril (cyclobenzaprine hydrochloride)

Most common side effects of the drugs, overall:

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Most common side effects of the drugs, in long term (1+ years) use:

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Drug effectiveness:

Nyquil:

  • not at all: 8.41 %
  • somewhat: 14.02 %
  • moderate: 38.32 %
  • high: 29.91 %
  • very high: 9.35 %

Flexeril:

  • not at all: 3.88 %
  • somewhat: 29.34 %
  • moderate: 36.93 %
  • high: 23.36 %
  • very high: 6.49 %

Want to compare Nyquil with Flexeril?

- Personalize this study to your gender and age (0-99+)

How to use the study?

DO NOT STOP MEDICATIONS without first consulting your doctor. If there are any serious or long term adverse effects discovered in the study, discuss the study with your doctor to ensure that proper medication management will be in place if applicable.

Related studies

Alternative drugs to, pros and cons of:

Browse all side effects of Nyquil:

a b c d e f g h i j k l m n o p q r s t u v w x y z

Browse all side effects of Flexeril:

a b c d e f g h i j k l m n o p q r s t u v w x y z

How the study uses the data?

The study is based on acetaminophen / dextromethorphan / doxylamine / pseudoephedrine and cyclobenzaprine hydrochloride (the active ingredients of Nyquil and Flexeril, respectively). Other drugs that have the same active ingredients (e.g. generic drugs or brand names) are also considered. Dosage of drugs is not considered in the study.

Who is eHealthMe?

With medical big data and proven AI/ML algorithms, eHealthMe provides a platform for everyone to run phase IV clinical trials. We study millions of patients and 5,000 more each day. Results of our real-world drug study have been referenced on 800+ peer-reviewed medical publications, including The Lancet, Mayo Clinic Proceedings, and Nature. Our analysis results are available to researchers, health care professionals, patients (testimonials), and software developers (open API).

WARNING, DISCLAIMER, USE FOR PUBLICATION

WARNING: Please DO NOT STOP MEDICATIONS without first consulting a physician since doing so could be hazardous to your health.

DISCLAIMER: All material available on eHealthMe.com is for informational purposes only, and is not a substitute for medical advice, diagnosis, or treatment provided by a qualified healthcare provider. All information is observation-only. Our phase IV clinical studies alone cannot establish cause-effect relationship. Different individuals may respond to medication in different ways. Every effort has been made to ensure that all information is accurate, up-to-date, and complete, but no guarantee is made to that effect. The use of the eHealthMe site and its content is at your own risk.

If you use this eHealthMe study on publication, please acknowledge it with a citation: study title, URL, accessed date.

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