Flexeril Side Effects and Allergic Reactions

Last Updated: June 3, 2020

Authored by Sharon Levy, MD, MPH

The most ordinary cyclobenzaprine side effect is drowsiness, dry mouth, and dizziness. According to NDA, clinical studies showed that Flexeril 10 mg side effects occur in up to 39% of patients with respect to drowsiness, dry mouth, and dizziness. The effects can be recurring and severe especially if the prescription is high or the drug is used inappropriately. Note that the side effects can be more adverse in elderly people, those aged 65 and above.

Common Cyclobenzaprine Side Effects

Although Amrix, the generic name for Flexeril, is one of the muscle relaxant believed to be less addictive, its side effects can’t be ignored. As mentioned above, cyclobenzaprine common side effects include:

  • Drowsiness
  • Dizziness
  • Dry mouth

The following Flexeril side effects have been reported in 1% to 3% of patients

  • Nausea
  • Irritabilityirritated woman
  • Mental acuity shriveled
  • Upper respiratory infection
  • Pharyngitis
  • Abdominal pain
  • Acid regurgitation
  • Constipation
  • Diarrhea

Other hostile reactions reported in less than 1% of patients include:

  • Cardiovascular – cardiac arrhythmia cardiovascular disease, palpitation, arrhythmia, and vasodilatation
  • Nervous system – seizures, ataxia, and dreaming, hallucinations, excitement, paraesthesia, vertigo, convulsions, muscle spasm, disorientation, insomnia, depressed mood, abnormal sensations, anxiety, dysarthria, tremors, hypertonia, agitation, psychosis, abnormal thinking, and visual disorder.
  • Digestive – instinctive reflex, gastritis, thirst, flatulence, anorexia, puffiness of the tongue, abnormal liver perform, diarrhea, epithelial duct pain, jaundice, and upset.
  • Hypersensitivity – hypersensitivity reaction, angioedema, pruritus, facial puffiness, urticaria, and rash.
  • Musculoskeletal – native weakness
  • Skin – sweating
  • Special Senses – ageusia and symptom
  • Urogenital – retention and urinary frequency

How Long do the Side Effects of Flexeril Last?

The longer the drug is consumed, the longer the side effects are experienced. The quantity taken is also directly proportional to the period of time it will take for one to experience the side effects. Cyclobenzaprine dosage should be taken as prescribed by the doctor. Taking higher doses than prescribed may cause the side effects to last even longer. Flexeril is intended as a short-term treatment that should last for a maximum of two weeks.

Can Cyclobenzaprine Side Effects Cause Death?

Restrictions are very clear as to who can take Flexeril. Few cases of death have been reported whereby patients had an overdose trying to achieve Flexeril high. When taken in excess or multiple ingestions, cyclobenzaprine is believed to shut down one’s respiratory system. Death will eventually occur.

Does Flexeril Cause Weight Gain?

Weight gain is not a common side effect for this medication. Depending on one’s metabolism, it is possible to gain or lose some weight. A large percentage of Flexeril weight gain is found among people who have been taking the drug for one month. The majority being female aged 50-59 old.
Flexeril long-term use does not have a big impact on weight gain.

Does Cyclobenzaprine Make Patients Sleepy or Tired?

Apparently, the drug has a frequent side effect that makes its users feel drowsy and dizzy. Some have reported having gotten very tired and also lessen their reaction time. Caution should be exercised when driving. But for the safety of other road users, cyclobenzaprine patients are not encouraged to drive.

Does Flexeril Lower Blood Pressure?

Cyclobenzaprine hydrochloride does not lower blood pressure. Instead, it can raise it in the event of taking an excessive amount of the drug. Some drugs like guanethidine can be less effective when used along with cyclobenzaprine. When used together, cyclobenzaprine can lower guanethidine effect by blocking the blood pressure, and therefore a patient’s blood pressure may go up.

Signs of Allergic Reactions to Cyclobenzaprine

Cyclobenzaprine can cause adverse allergic reactions. Here are the symptoms:

  • Hivesman with allergic hives and rash
  • Difficult breathing
  • Swelling of a patient’s face, lips, tongue, or throat
  • Skin rash
  • Severe dizziness
  • Tightness in chest
  • Changes in the skin color of the face

Ignoring these symptoms and going ahead with the drug can be fatal.

Preventing Flexeril Side Effects

Cyclobenzaprine side effects listed in this article apart from the common ones are not experienced by every patient. Note that these side effects can be mild or severe, temporary or permanent. It is important to take the following necessary precautions seriously.

  • Do not take Flexeril drugs prescribed to another patient
  • Allergic reactions should not be ignored
  • Patients with glaucoma should consult with their doctor on how this medication can affect their health
  • The use of cyclobenzaprine for periods longer than 3 weeks is not recommended
  • People with liver disease or reduced liver function should stay away from Flexeril
  • Cyclobenzaprine should not be combined with other medications that act on serotonin. If combined, severe reactions are high to occur. Take the Flexeril drug test to make sure the substance is removed from the system before taking the medications that can potentially interact with cyclobenzaprine. Note that even the relatively safe interactions like Cyclobenzaprine and ibuprofen can also cause side effects in people with specific conditions and personal tolerance.
  • Children under the age of 15 and persons aged 65 and older should not use Flexeril

However, there is another dangerous effect of Cyclobenzaprine apart from those listed in this article – it is the addiction to this muscle relaxant. The long-term abuse and dependence on Flexeril require the professional approach of the rehab clinic medical professionals. They will provide the medical treatment for abusing drugs as well as the aftercare to ensure the complete recovery.

Page Sources

  1. David Shprecher, Colgan T Sloan, Benson Sederholm, Neuropsychiatric side effects of cyclobenzaprine, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3669814/
  2. J Mestres, SA Seifert, TI Oprea, Linking Pharmacology to Clinical Reports: Cyclobenzaprine and Its Possible Association With Serotonin Syndrome, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3809033/

Published on: November 30th, 2018

Updated on: June 3rd, 2020

About Author

Sharon Levy, MD, MPH

After successful graduation from Boston University, MA, Sharon gained a Master’s degree in Public Health. Since then, Sharon devoted herself entirely to the medical niche. Sharon Levy is also a certified addiction recovery coach.


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  • Terri Dunn
    Is weight gain common