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

Summary:

We compare the side effects and drug effectiveness of Flexeril and Codeine. The phase IV clinical study is created by eHealthMe based on reports (from sources including the FDA) of 141,849 people who take Flexeril and Codeine, and is updated regularly.

What is Flexeril?

Flexeril has active ingredients of cyclobenzaprine hydrochloride. It is often used in muscle spasms. eHealthMe is studying from 38,307 Flexeril users. Check the latest studies of Flexeril.

What is Codeine?

Codeine has active ingredients of codeine sulfate. It is often used in pain. eHealthMe is studying from 42,342 Codeine users. Check the latest studies of Codeine.

On Apr, 05, 2026

141,849 people who take Flexeril and Codeine are studied.

Flexeril vs Codeine drug comparison reports.

Drugs being compared in this study:

  • Flexeril (cyclobenzaprine hydrochloride)
  • Codeine (codeine sulfate)

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:

Flexeril:

  • not at all: 3.85 %
  • somewhat: 29.42 %
  • moderate: 36.82 %
  • high: 23.44 %
  • very high: 6.46 %

Codeine:

  • not at all: 2.7199999999999998 %
  • somewhat: 25.94 %
  • moderate: 36.4 %
  • high: 26.78 %
  • very high: 8.16 %

Want to compare Flexeril with Codeine?

- 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 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

Browse all side effects of Codeine:

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 cyclobenzaprine hydrochloride and codeine sulfate (the active ingredients of Flexeril and Codeine, 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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