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Last Updated: 9/1/2026

Cyclobenzaprine hydrochloride

Drug Name(s): Amrix, Flexmid, Flexeril, generic, Tonmya

Class: Muscle relaxants

Cyclobenzaprine hydrochloride is a skeletal muscle relaxant used to treat fibromyalgia. Most are used off-label, but a new brand has been FDA-approved to treat fibromyalgia.

Dosage

Form(s): tablet  

Amrix, generic: ER capsules 15 mg or 30 mg once a day 

Generic: IR tablets 5 mg to 10 mg three times a day 

For Tonmya: 1 2.8mg tablet under the tongue once a day to start, then 2 2.8 tablets under the tongue once a day 


Special Instructions

Do not drive or perform other potentially dangerous activities until you know whether the medication will impair your ability to do them safely

Take 2 to 3 hours before bed to reduce morning grogginess.

Talk to your doctor before stopping the drug. Your dose may need to be slowly reduced.

Potential Side Effects

Drowsiness, dizziness, dry mouth, constipation, nausea, indigestion, sore throat, headache 

For Tonmya: mouth discomfort, including numbness, tingling, bad taste, pain, canker sore 


Be Aware

Be sure your doctor knows if you have liver problems or are over 65 years old, which may affect your dosage. 

Do not take with antidepressants, including monoamine oxidase inhibitors (or within 14 days after stopping one), selective serotonin reuptake inhibitors (SSRIs), serotonin norepinephrine reuptake inhibitors (SNRIs) or tricyclic antidepressants. 

Do not take if you are or may become pregnant. Tell your doctor if you are breastfeeding. 

Tell your doctor if you have had a heart attack or other heart problems.  

Tell your doctor if you have an overactive thyroid. 

Tell your doctor if you have had glaucoma, seizures, liver disease or trouble urinating.  

Do not take with tramadol or other drugs that affect the central nervous system. 

For Tonmya: Do not take if you have hyperthyroidism or if you are recovering from a cardiovascular event.  


The Arthritis Foundation’s Drug Guide is meant for education — not self-medicating. The Arthritis Foundation does not endorse any products mentioned in this guide. While we endeavor to keep the information up to date, we make no representations or warranties about the completeness of the information provided.