Prescription medication · Muscle Relaxant
cyclobenzaprine
Also sold as Flexeril, Amrix. This medicine treats muscle spasms caused by painful conditions.
Data updated 2026-05-15
- 47,426
- FDA reportsOften reported
- 17
- InteractionsSeveral interactions
- $0.02
- Generic price (NADAC)
What the data shows
cyclobenzaprine (Flexeril) is a prescription Muscle Relaxant, reported at a middle-of-the-pack volume (47,426 FDA reports), with 17 documented drug interactions.
Reporting volume reflects how widely a drug is used and studied, not how dangerous it is, a FAERS report documents a temporal association, never proof of cause.
cyclobenzaprine (Flexeril) is a prescription Muscle Relaxant. This medicine treats muscle spasms caused by painful conditions.
Cyclobenzaprine is a muscle relaxant. It helps relieve muscle spasms and pain.
Verify with FDA → · CMS NADAC pricing →
Drug Pricing (NADAC)
Generic Price
$0.02/unit
Generic Available
Yes (13 manufacturers)
Pricing data from NADAC (CMS), effective December 18, 2024. Compare all drug costs →
What it does
This medicine treats muscle spasms caused by painful conditions.
Common side effects
Drowsiness, Dry mouth, Fatigue
Key warnings
You should not take this medicine if you are allergic to any of its ingredients.
The sections below are summarized in plain English from cyclobenzaprine's FDA-approved prescribing information. They describe what the official label says, and are not personal medical advice.
How It Works
Cyclobenzaprine works in the brain and spinal cord to relax your muscles. It reduces muscle spasms, which helps to relieve pain and improve movement. It does not directly work on the muscles themselves.
How to Take It
The usual dose is 5 mg three times a day. Your doctor may increase the dose to 10 mg three times a day, depending on how you respond to the medicine. You can take this medicine with or without food. Do not take it for longer than 2 or 3 weeks.
This is a plain-language summary of cyclobenzaprine's FDA labeling, not individualized dosing advice. Ask a pharmacist or prescriber before changing how you take this medication.
Pregnancy & Breastfeeding
It is not known if cyclobenzaprine can harm an unborn baby. Talk to your doctor if you are pregnant, planning to become pregnant, or breastfeeding.
This is a plain-language summary of cyclobenzaprine's FDA labeling, not individualized advice. Ask a pharmacist or prescriber about pregnancy or breastfeeding on this medication.
Missed Dose
If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and continue with your regular schedule.
This is a plain-language summary of cyclobenzaprine's FDA labeling, not individualized advice. Ask a pharmacist or prescriber what to do about your specific missed dose.
Storage
Store at room temperature, between 68°F and 77°F, in a tightly closed, light-resistant container.
Side Effects (from patient reports)
Based on 47,426 FDA adverse event reports.
Most-reported reactions
Adverse reactions in FAERS for cyclobenzaprine, by number of reports
- Pain
Pain
4,873 reports
- Tiredness
Tiredness
3,808 reports
- Feeling sick to your stomach
Feeling sick to your stomach
3,304 reports
- Headache
Headache
3,292 reports
- Long-term kidney problems
Long-term kidney problems
2,749 reports
- Diarrhea
Diarrhea
2,426 reports
- Fall
Fall
2,334 reports
- Joint pain
Joint pain
2,325 reports
- Harm from different substances
Harm from different substances
2,289 reports
- Difficulty breathing
Difficulty breathing
2,099 reports
What this shows Bars show how often each reaction was reported, not how likely it is to happen, a report records a temporal association, never proof that the drug caused it.
Reports over time
Adverse-event reports filed for cyclobenzaprine each year to the FDA Adverse Event Reporting System (FAERS).
Year-to-year volume tracks usage, prescribing, and scrutiny, not a change in per-patient risk. Source: FDA FAERS.
Where cyclobenzaprine sits
cyclobenzaprine has more FDA adverse-event reports than 72% of the drugs FAERS tracks. A high position reflects how widely a drug is used and watched, not how dangerous it is.
Percentile across all drugs PlainMeds tracks by FAERS report volume. The dot is cyclobenzaprine; the line is the median (50th percentile).
FDA Adverse Event Report Analysis
Detailed analysis of 47,426 reports from the FDA Adverse Event Reporting System (FAERS). Reports span 2003–2025.
Total Reports
47,426
Reports Mentioning Death
6,863
14.5% of reports — not proof of cause
Hospitalization Reports
13,293
Top Indication
Product Used For Unknown Indication
Gender Distribution
Age Distribution
Most Reported Adverse Reactions (FAERS)
| # | Reaction | Reports |
|---|---|---|
| 1 | PAIN | 4,871 |
| 2 | FATIGUE | 3,808 |
| 4 | NAUSEA | 3,303 |
| 5 | HEADACHE | 3,292 |
| 6 | CHRONIC KIDNEY DISEASE | 2,749 |
| 8 | DIARRHOEA | 2,426 |
| 9 | FALL | 2,334 |
| 10 | ARTHRALGIA | 2,325 |
| 11 | TOXICITY TO VARIOUS AGENTS | 2,289 |
| 12 | DYSPNOEA | 2,099 |
| 13 | CONSTIPATION | 2,064 |
| 14 | BACK PAIN | 2,048 |
| 15 | COMPLETED SUICIDE | 1,953 |
| 16 | DIZZINESS | 1,936 |
| 17 | ANXIETY | 1,929 |
Reactions in Death Reports
Reactions in Hospitalization Reports
Source: FDA FAERS (Adverse Event Reporting System) FDA FAERS (Adverse Event Reporting System) Reports are voluntary and do not establish causation
Serious Warnings
You should not take this medicine if you are allergic to any of its ingredients. You should not take this medicine if you are taking a monoamine oxidase (MAO) inhibitor or have taken one in the past 14 days. Taking cyclobenzaprine with an MAO inhibitor can cause serious problems, including seizures and death. Also, do not take it if you have heart problems or an overactive thyroid.
Known Drug Interactions
Anticholinergic Drugs Concomitant treatment with clozapine and other drugs with anticholinergic activity (e.g., benztropine, cyclobenzaprine, diphenhydramine) can increase the risk for anticholinergic toxicity and severe gastrointestinal adverse reactions related to hypomotility.
Mechanism: Both drugs have similar side effects that can slow down your digestive system and cause confusion or dry mouth. Combining them makes these side effects much more likely and can lead to severe constipation or toxicity.
What to do: Your doctor should monitor you for signs of toxicity or severe stomach issues. They may need to adjust your dose or choose a different medication to avoid these complications.
Examples: Selective serotonin reuptake inhibitors (SSRIs), serotonin and norepinephrine reuptake inhibitors (SNRIs), tricyclic antidepressants (TCAs), triptans, 5-HT3 receptor antagonists, drugs that affect the serotonin neurotransmitter system (e.g., mirtazapine, trazodone, tramadol), certain muscle relaxants (i.e., cyclobenzaprine, metaxalone), monoamine oxidase inhibitors (those intended to treat psychiatric disorders and also others, such as linezolid and intravenous methylene blue). Due to the risk of respiratory depression with concomitant use of skeletal muscle relaxants and...
Mechanism: Taking these drugs together increases the risk of dangerous slowing of your breathing. They can also cause a serious buildup of a brain chemical called serotonin.
What to do: Use these medications together only if your doctor determines it is necessary. Monitor closely for extreme sleepiness or trouble breathing.
Product Clinical Comment on Concomitant Use [See Contraindications (4.1)] ; Predominant Effect/Risk [Hypertensive Reaction (HR) [See Warnings and Precautions (5.3)] ; or Serotonin Syndrome (SS) [See Warnings and Precautions (5.7)] ] Altretamine Use with caution If not otherwise specified in this table, consider avoiding concomitant use (see also information on medication-free intervals , use agent at the lowest appropriate dose, monitor for effects of the interaction, advise the patient to report potential effects, and be prepared to discontinue the agent and treat effects of the...
Mechanism: Taking these drugs together can lead to a life-threatening reaction or a sudden, very high increase in blood pressure.
What to do: It is best to avoid this combination, and your doctor may need to adjust your treatment plan to use a different medicine.
Serotonergic Drugs The concomitant use of opioids with other drugs that affect the serotonergic neurotransmitter system, such as selective serotonin reuptake inhibitors (SSRIs), serotonin and norepinephrine reuptake inhibitors (SNRIs), tricyclic antidepressants (TCAs), tryptans, 5-HT3 receptor antagonists, drugs that affect the serotonin neurotransmitter system (e.g., mirtazapine, trazodone, tramadol), certain muscle relaxants (i.e., cyclobenzaprine, metaxalone), and monoamine oxidase (MAO) inhibitors (those intended to treat psychiatric disorders and also others, such as linezolid and...
Mechanism: Both drugs increase serotonin levels in the brain, which can cause a serious reaction called serotonin syndrome.
What to do: Your doctor should monitor you for symptoms like confusion or a fast heartbeat if you use these together.
Examples: Selective serotonin reuptake inhibitors (SSRIs), serotonin and norepinephrine reuptake inhibitors (SNRIs), tricyclic antidepressants (TCAs), triptans, 5-HT3 receptor antagonists, drugs that affect the serotonin neurotransmitter system (e.g., mirtazapine, trazodone, tramadol), certain muscle relaxants (i.e., cyclobenzaprine, metaxalone), monoamine oxidase (MAO) inhibitors (those intended to treat psychiatric disorders and also others, such as linezolid and intravenous methylene blue).
Mechanism: Both drugs increase serotonin levels in the brain, which can cause a serious and potentially dangerous reaction.
What to do: Talk to your doctor about the risks and watch for symptoms like confusion, shivering, or a fast heartbeat.
This is a plain-language summary of interactions documented in FDA labeling, not individualized advice. Ask a pharmacist or prescriber before combining medications.
Common Questions
Can I drive while taking this medicine?
Can I drink alcohol while taking this medicine?
How long does it take for this medicine to work?
Can I take this medicine with other medicines?
What should I do if I have side effects?
Can I stop taking this medicine suddenly?
Is cyclobenzaprine a painkiller?
Can I take cyclobenzaprine long term?
What do the different colored pills mean?
Can I crush or split the tablets?
What are the common side effects of cyclobenzaprine?
Does cyclobenzaprine interact with other medications?
What drug class is cyclobenzaprine?
Is cyclobenzaprine safe during pregnancy?
Related Medications in Muscle Relaxant
Other drugs grouped near cyclobenzaprine - same-class peers and common alternatives.
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What the FDA Data Shows for cyclobenzaprine
The FDA label for cyclobenzaprine (sold under brand names such as Flexeril, Amrix) classifies it as a prescription-only medication in the Muscle Relaxant class. This medicine treats muscle spasms caused by painful conditions. Official labeling lists 4 commonly reported side effects, including Drowsiness, Dry mouth, Fatigue.
Post-market surveillance from the FDA Adverse Event Reporting System (FAERS) captures real-world experience. For this drug, FAERS contains 47,426 voluntary reports. The database also lists 17 documented drug interactions derived from FDA labeling, with the top-flagged interaction rated moderate severity. NADAC pricing from CMS shows a generic unit cost of $0.02.
Report counts do not establish causation, a FAERS entry documents a temporal association, not proof that the drug produced the outcome. Widely prescribed medications naturally accumulate more reports than niche therapies, so raw totals must be interpreted alongside total exposure. Shortage status, recall history, and patent information further shape supply and switching decisions. This page summarizes public FDA data for educational purposes only and is not a substitute for professional medical advice, always consult a licensed healthcare provider before starting, stopping, or changing any medication.
Data Sources
Drug labeling: FDA Drug Labels (SPL/DailyMed). Adverse events: FDA Adverse Event Reporting System (FAERS). Pricing: CMS National Average Drug Acquisition Cost (NADAC).
FAERS reports are voluntary and do not establish causation. Drug interactions are derived from FDA labeling and clinical references. Always consult a healthcare professional before making medication decisions.
Last updated: December 5, 2025
Read our methodology - how this data is sourced, computed, and verified.
Data currency: FDA FAERS adverse-event reports through 2025, CMS NADAC acquisition-cost pricing effective December 2024, compiled and last refreshed May 2026. See our methodology for per-source dates and refresh cadence. Spot a figure that looks wrong? Report a correction.
All federal data sources used on this page
- FDA Orange Book - approved drug products with therapeutic equivalence. accessdata.fda.gov/cder/ob
- FDA DailyMed - NIH-hosted drug labeling for FDA-approved meds. dailymed.nlm.nih.gov
- FDA Adverse Event Reporting System (FAERS) - post-marketing safety surveillance. fda.gov/drugs/faers
- NLM RxNorm - standardized clinical drug nomenclature. nlm.nih.gov/research/umls/rxnorm
- CMS Medicare Part B Drug Average Sales Price Files - federal drug pricing data. cms.gov/medicare/part-b-drugs/asp
- FDA Drug Shortages Database - current and resolved drug shortage tracking. accessdata.fda.gov/drugshortages