Overview

Flexeril is a brand name historically used for the medicine cyclobenzaprine, a centrally acting skeletal muscle relaxant. In the United States it is prescribed short term to ease acute muscle spasm and related pain, usually together with rest, heat/ice, and physical therapy. Extended-release cyclobenzaprine capsules have been sold under brand names such as Amrix.

  • Active ingredient: Cyclobenzaprine
  • Therapeutic class: Muscle relaxant for relief of acute musculoskeletal spasm
  • Common strengths available: Immediate-release tablets 5 mg and 10 mg; extended-release capsules 15 mg and 30 mg
  • Typical course length: Short term only, generally 2 to 3 weeks
  • Not established in: Children under 15 years

If you need to jump to interaction details, go directly to Interactions. For urgent safety issues, see Side effects.

What Flexeril treats

Cyclobenzaprine helps reduce muscle spasm and stiffness resulting from short-term musculoskeletal problems such as strains and sprains. It does not treat nerve pain or chronic spasticity from neurologic conditions. It is most effective when paired with conservative measures like activity modification and physical therapy.

Related categories: Muscle relaxants, Pain relief adjuncts.

How to take it

Always follow your prescriber's instructions and the pharmacy label. Take doses at the same time each day.

  • Immediate-release (IR) tablets: Commonly 5 mg three times daily; some patients may require up to 10 mg three times daily. Do not exceed a total of 30 mg per day.
  • Extended-release (ER) capsules (e.g., 15 mg): Often 15 mg once daily; some may need 30 mg once daily. Swallow whole; do not crush or chew. You may sprinkle contents on applesauce and swallow immediately without chewing if directed.
  • Duration: Typically 2 to 3 weeks; longer use has not been shown to improve outcomes for acute spasm.
  • Liver impairment/older adults: Lower doses or less frequent dosing may be required. Discuss with your clinician.
  • With or without food: Either is acceptable; be consistent.

For storage details, skip to Storage. For overdose, go to Overdose.

Precautions

Before using cyclobenzaprine, tell your health care provider about your full medical history and all medicines you take.

  • May cause drowsiness, dizziness, and blurred vision. Avoid driving or operating machinery until you know your response.
  • Alcohol and other sedatives can intensify drowsiness and increase risk of falls or accidents.
  • Tell your clinician if you have liver disease, glaucoma, difficulty urinating, or an enlarged prostate.
  • Use in pregnancy or while breastfeeding should be discussed with a clinician; human data are limited.
  • Older adults may be more sensitive to anticholinergic effects like dry mouth and confusion.

If you have conditions listed in Who should not take it, do not use cyclobenzaprine unless your prescriber determines it is appropriate.

Who should not take it

Do not use cyclobenzaprine if any of the following apply to you:

  • Recent heart attack, significant arrhythmia, or heart block
  • Hyperthyroidism
  • Congestive heart failure or severe cardiac disease
  • Use of an MAO inhibitor within the last 14 days (e.g., isocarboxazid, phenelzine, tranylcypromine, linezolid, selegiline, rasagiline)

If unsure about your situation, review your history with a clinician before starting therapy.

Possible side effects

Seek emergency help for signs of an allergic reaction: hives, trouble breathing, or swelling of the face, lips, tongue, or throat.

Stop the medicine and contact a clinician right away for any of the following serious effects:

  • Fast or irregular heartbeat, chest pain, or pressure
  • Sudden numbness or weakness on one side, trouble speaking, or balance problems
  • Symptoms of serotonin syndrome: agitation, hallucinations, fever, sweating, shivering, rapid heartbeat, muscle rigidity or twitching, incoordination, nausea, vomiting, or diarrhea

More common, usually mild effects include:

  • Drowsiness or fatigue
  • Dry mouth
  • Headache or dizziness
  • Upset stomach, constipation, or nausea

Report persistent or severe symptoms to your health care provider. For interactions that may raise risk of side effects, see Interactions.

Drug and substance interactions

Combining cyclobenzaprine with other sedating or serotonergic agents can increase side effect risks.

  • Other central nervous system depressants: opioid pain medicines, benzodiazepines, sleep aids, other muscle relaxants, alcohol, certain antihistamines
  • Serotonergic medicines: SSRIs, SNRIs, TCAs, MAO inhibitors, tramadol, meperidine, linezolid, triptans, St. John's wort
  • Medicines with strong anticholinergic effects: some allergy or cold remedies, medicines for overactive bladder, and certain drugs for motion sickness or irritable bowel
  • Drugs for Parkinson disease or bronchodilators can sometimes have additive side effects; consult your clinician or pharmacist

Always provide a complete list of prescription drugs, OTC products, and supplements to your clinician and pharmacist. If you recently used an MAOI, see Who should not take it.

If you miss a dose

Take it when remembered unless it is close to the time for your next scheduled dose. If it is almost time, skip the missed dose. Do not double up.

Overdose

Call emergency services or your local poison control center right away if an overdose is suspected. Symptoms may include severe drowsiness, vomiting, rapid heartbeat, tremors, agitation, confusion, or hallucinations. Large overdoses can be life threatening.

For urgent symptom guidance, also review Possible side effects.

Storage

  • Keep out of reach of children and pets.
  • Store at room temperature, ideally 59 to 86 degrees F (15 to 30 degrees C).
  • Keep the container tightly closed and away from moisture.
  • Discard unused or expired medicine according to pharmacy or community take-back guidance.

Alternatives and similar medications

Several other muscle relaxants may be considered if cyclobenzaprine is not a fit. Selection depends on medical history, side effect tolerance, and concurrent medications. Discuss options with your prescriber.

  • Tizanidine (Zanaflex): Often used for spasm; can lower blood pressure and cause sedation. Interacts with CYP1A2 inhibitors like ciprofloxacin.
  • Methocarbamol (Robaxin): Sedation possible; commonly used for acute musculoskeletal conditions.
  • Baclofen: More often used for spasticity of neurologic origin; can cause dizziness and weakness.
  • Metaxalone (Skelaxin): May be less sedating for some; can affect liver enzymes and is typically pricier.
  • Carisoprodol (Soma): Sedating and habit forming; Schedule IV controlled substance in the USA, generally not first line.
  • Diazepam: A benzodiazepine with muscle relaxant effects; dependence and sedation risks limit use for simple acute spasm.

For how these compare in cost in the USA, see Typical prices.

Typical prices in the USA (USD)

Approximate out-of-pocket retail prices vary by pharmacy, region, brand vs generic, and discount programs. Insurance copays can be much lower. The ranges below are rough cash estimates for 30 days unless otherwise noted.

  • Cyclobenzaprine IR 5 mg or 10 mg tablets (generic): about $5 to $20 for 30 tablets.
  • Cyclobenzaprine ER 15 mg capsules (generic if available): roughly $150 to $400 for 30 capsules.
  • Amrix (brand ER 15 mg): can exceed $600 to $900 for 30 capsules.
  • Tizanidine 4 mg (generic): about $6 to $25 for 30 tablets or capsules.
  • Methocarbamol 750 mg (generic): around $8 to $30 for 40 to 60 tablets.
  • Baclofen 10 mg (generic): approximately $6 to $20 for 30 tablets.
  • Metaxalone 800 mg (generic or brand): often $30 to $200 for 30 tablets, depending on supply and discounts.
  • Carisoprodol 350 mg (generic): typically $8 to $30 for 30 tablets, but controlled-substance rules apply.

Tip: Pharmacy discount cards and price comparison tools can significantly reduce cost. Always verify current pricing at your local pharmacy.

At-a-glance summary

  • Relevant to: Muscle relaxants, adjunctive pain relief
  • Available dosage highlighted in original page: 15 mg
  • Best used with rest and physical therapy for acute musculoskeletal conditions

Have more questions? Start at the Overview or jump back to the top.