Flexeril and Fentora drug interactions - a phase IV clinical study of FDA data

Summary:

Drug interactions are reported among people who take Flexeril (cyclobenzaprine hydrochloride) and Fentora (fentanyl citrate). Common drug interactions include arthralgia among females and drug effect decreased among males.

The phase IV clinical study analyzes what interactions people have when they take Flexeril and Fentora. It is created by eHealthMe based on reports of 18 people who take the same drugs from the FDA, 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 38,308 Flexeril users. Check the latest studies of Flexeril.

What is Fentora?

Fentora has active ingredients of fentanyl citrate. eHealthMe is studying from 26,490 Fentora users. Check the latest studies of Fentora.

eHealthMe: drug outcomes in the real world

eHealthMe runs one of the largest post-marketing drug safety studies in the world. We study millions of patients and 5,000 more each day. Our data-driven phase IV clinical trials have been referenced on 800+ peer-reviewed medical publications including The Lancet, Mayo Clinic Proceedings, and Nature. Tools to study our phase IV findings are available to the public, anonymous and free >>>.

On Aug, 23, 2026

18 people who take Flexeril and Fentora together, and have interactions are studied.

What are the common drug interactions of Flexeril and Fentora, by gender? *:

female:

Arthralgia (joint pain)
Asthenia (weakness)
Atrophy (wasting away of a part of the body)
Bursitis (inflammation of a bursa, typically one in the knee, elbow, or shoulder)
Depression
Fall
Insomnia (sleeplessness)
Joint effusion (presence of extra fluid in joint covering)
Myofascial pain syndrome (a painful condition that affects the muscles and the sheath of the tissue)
Osteoporosis (bones weak and more likely to break)

male:

Drug effect decreased
Delirium (wild excitement)
Therapeutic response decreased (less preventive response)
Drug withdrawal syndrome (interfere with normal social, occupational, or other functioning. are not due to another medical condition, drug use, or discontinuation)
Serotonin syndrome (occurs when two drugs that affect the body's level of serotonin are taken together at the same time)
Back injury
Dental caries
Pain
Confusional state
Convulsion (muscles contract and relax rapidly and repeatedly, resulting in an uncontrolled shaking of the body)

What are the common drug interactions of Flexeril and Fentora, by age (0-1 to 60+)? *:

0-1:

n/a

2-9:

n/a

10-19:

n/a

20-29:

n/a

30-39:

n/a

40-49:

Delirium (wild excitement)
Drug withdrawal syndrome (interfere with normal social, occupational, or other functioning. are not due to another medical condition, drug use, or discontinuation)
Serotonin syndrome (occurs when two drugs that affect the body's level of serotonin are taken together at the same time)
Pain
Stomatitis (inflammation of mucous membrane of mouth)
Confusional state
Incoherent (talking in a confused and unclear way)
Drug ineffective
Mouth haemorrhage (bleeding from mouth)

50-59:

Asthenia (weakness)
Atrophy (wasting away of a part of the body)
Bursitis (inflammation of a bursa, typically one in the knee, elbow, or shoulder)
Contusion (a type of hematoma of tissue in which capillaries)
Depression
Fall
Insomnia (sleeplessness)
Joint effusion (presence of extra fluid in joint covering)
Local swelling (swelling at the site of some application of substance or injury)
Myofascial pain syndrome (a painful condition that affects the muscles and the sheath of the tissue)

60+:

Drug effect decreased
Dental caries
Therapeutic response decreased (less preventive response)
Dyspnoea (difficult or laboured respiration)
Haemoglobin decreased
Metastases to lymph nodes (cancer spreads to lymph node)

What are the existing conditions these people have? *

Back Pain: 5 people, 27.78%
Pain: 5 people, 27.78%
Bone Pain: 3 people, 16.67%
Thyroid Diseases: 2 people, 11.11%
Headache (pain in head): 2 people, 11.11%
Diabetes: 2 people, 11.11%
Drowsiness: 2 people, 11.11%
Back Injury: 2 people, 11.11%
Neuralgia (pain in one or more nerves): 2 people, 11.11%
Sleep Disorder: 2 people, 11.11%

* Approximation only. Some reports may have incomplete information.

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