Flexeril (Cyclobenzaprine): Uses, Side Effects, Dosages

Flexeril (cyclobenzaprine) is a muscle relaxer prescribed for very tight muscle spasms, as well as pain and discomfort from muscle injuries. It is generally used short term along with physical therapy and rest for acute injuries, such as tendon or ligament sprains and muscle strains. 

Flexeril is actually the brand-name version of the drug, and it is discontinued. However, the name is still often used interchangeably with cyclobenzaprine (the generic name). An extended-release version is available both as a generic or under the brand name Amrix.

In this article, you'll learn all about Flexeril, how it works, the proper Flexeril dosage, side effects and precautions, and what drugs shouldn't be combined with cyclobenzaprine.

How Flexeril Works

Flexeril doesn't work directly on the muscles. Instead, it works in the central nervous system—particularly the brain stem—to relieve spasms.

By relaxing ultra-tight muscles, Flexeril may help you make faster progress with your home exercise program.

Flexeril Dosage

As with any medication, you should stick to the Flexeril dosage prescribed by your healthcare provider. This drug is meant to be used for between two and three weeks at a time.

Generally, Flexeril directions stay to take three tablets a day.

• Immediate-release tablets contain either 5 milligrams (mg) or 10 mg
• Extended-release tablets contain either 15 mg or 30 mg

Flexeril dosages for off-label (non-approved) uses such as fibromyalgia and sciatica are not established. Fibromyalgia studies have used doses between 1 mg and 4 mg before bed.

If you think you need more of this drug, talk to your healthcare provider. Don't increase the dosage on your own.

Flexeril Side Effects and Risks

Cyclobenzaprine carries a risk of side effects and may not be safe for some people. It can also interact negatively with certain drugs.

Side Effects

Some common side effects of Flexeril include:

• Dry mouth
• Drowsiness
• Dizziness
• Tiredness
• Constipation
• Blurred vision
• Unpleasant taste
• Nervousness
• Confusion
• Abdominal pain or discomfort

Drowsiness is so common that Flexeril is sometimes prescribed for improving sleep, especially in people with chronic pain disorders such as fibromyalgia.

Serious side effects are rare, but if they do occur they require prompt medical attention. These include:

• Mental and mood changes (e.g., hallucinations, confusion)
• Difficulty urinating
• Dark urine
• Fast, pounding, and/or irregular heartbeat
• Fainting
• Yellowing of the eyes and/or skin (jaundice)
• Stomach and/or abdominal pain
• Persistent nausea, vomiting, and/or lack of appetite
• Seizures
• Loss of coordination

Older people are more sensitive to Flexeril side effects.

Allergies and Precautions

Flexeril contains inactive ingredients that sometimes cause allergic reactions. Especially if you have known drug allergies, be sure to talk to your healthcare provider and pharmacist about this before taking this drug.

To avoid possible complications of Flexeril, let your healthcare provider know if you have:

• Liver disease
• Thyroid problems
• Depression, bipolar disorder, or other mental health conditions
• A seizure disorder
• Heart problems
• Glaucoma
• Difficulty urinating now or in the past

Safety in children under 15 hasn't been established.

What to Avoid While Taking Flexeril

Some medications shouldn't be taken together due to negative interactions. Flexeril shouldn't be taken with:

• Opioids: Vicodin (hydrocodone/acetaminophen), codeine, OxyContin (oxycodone)
• Tricyclic antidepressants: Amitriptyline, Norpramin (desipramine), Pamelor (nortriptyline)
• Serotonin norepinephrine reuptake inhibitor (SNRI) antidepressants: Cymbalta (duloxetine), Savella (milnacipran)
• Other antidepressants: Wellbutrin (bupropion), Ultram (tramadol)
• MAO Inhibitors (MAOIs): Marplan (isocarboxazid), Nardil (phenelzine), Emsam (selegiline)
• Anticholinergics: Atropen (atropine), Cogentin (beztropine mesylate), Enablex (darifenacin), Lotronex (alosetron)
• Voltage gated potassium channel blockers: Firdapse/Ruzurgi (amifampridine), Ampyra (dalfampridine)
• Anti-anxiety drugs: Xanax (alprazolam), Klonopin (clonazepam), Valium (diazepam)
• Sedatives (sleeping pills): Ambien (zolpidem), Lunesta (eszopiclone), Luminal (phenobarbital), Xyrem (sodium oxybate)
• Sedating antihistamines/cough suppressants: Benadryl (diphenhydramine), Solotuss (carbetapentane), Chlor-Trimeton (chlorpheniramine), Zyrtec (cetirizine)
• COMT inhibitors for Parkinson's disease: Atmet/Duopa (carbidopa/levodopa), Comtan (entacapone), Tasmar (tolcapone)
• Anti-seizure drugs: Lyrica (pregabalin), Neurontin (gabapentin)

Summary

Flexeril (cyclobenzaprine) is a muscle relaxer that works on the central nervous system. It comes in multiple dosages plus regular and extended-release forms.

Watch for side effects such as drowsiness, dizziness, and confusion. Severe side effects such as hallucinations, urine changes, jaundice, and seizures need immediate medical attention.

Don't take this drug if you're pregnant, breastfeeding, or under age 15. Tell you healthcare provider about all your medical conditions and other medications.