Norflex
Muscle Relaxant for Musculoskeletal Pain Relief
Quick Facts About Norflex
Key Takeaways
- Norflex is a centrally acting muscle relaxant that relieves pain from muscle strains, back injuries, and whiplash
- The standard adult dose is one 100 mg extended-release tablet twice daily (morning and evening) – tablets must be swallowed whole
- Common side effects include drowsiness, dry mouth, and blurred vision due to anticholinergic properties
- Norflex is contraindicated in patients with myasthenia gravis, narrow-angle glaucoma, and gastrointestinal or urinary obstruction
- Alcohol and opioid analgesics can increase sedation and should be used with extreme caution alongside Norflex
What Is Norflex and What Is It Used For?
Quick Answer: Norflex (orphenadrine citrate) is a prescription muscle relaxant that works on the central nervous system to relieve muscle pain and spasm. It is used for acute musculoskeletal conditions including muscle strains, lower back pain (lumbago), skeletal injuries, and neck pain (whiplash/torticollis).
Norflex contains the active ingredient orphenadrine citrate, a centrally acting skeletal muscle relaxant that has been used in clinical practice for several decades. Unlike peripherally acting muscle relaxants that work directly on the muscles, orphenadrine acts primarily within the central nervous system – specifically on the brainstem reticular formation and the spinal cord – to reduce excessive muscle tone and spasm. This central mechanism of action distinguishes it from drugs like dantrolene, which acts on the muscle fibre itself.
In addition to its muscle relaxant properties, orphenadrine possesses mild analgesic (pain-relieving) effects that are independent of its action on muscle tone. Research suggests this analgesic component may involve modulation of N-methyl-D-aspartate (NMDA) receptor activity, which plays a role in pain signal transmission. This dual action – muscle relaxation combined with pain relief – makes Norflex particularly useful for treating painful musculoskeletal conditions where both muscle spasm and pain are contributing factors.
Orphenadrine also has notable anticholinergic (antimuscarinic) and antihistaminic properties. These pharmacological characteristics are responsible for both some of its therapeutic effects and several of its side effects, including dry mouth, blurred vision, and drowsiness. The anticholinergic activity means that Norflex should be used with particular caution in certain patient populations, especially those with conditions that can be worsened by reduced parasympathetic nervous system activity.
Common clinical indications for Norflex include acute muscle strains from sports injuries or physical exertion, acute lower back pain (lumbago) with associated muscle spasm, skeletal injuries where muscle guarding contributes to pain, and cervical muscle spasm due to whiplash injury or torticollis. It is typically prescribed as a short-term adjunctive therapy alongside rest, physical therapy, and other measures for the relief of acute musculoskeletal discomfort.
How Does Norflex Work?
The precise mechanism by which orphenadrine produces skeletal muscle relaxation in humans is not fully established, though several pathways have been identified. The drug appears to act at multiple levels within the central nervous system. At the brainstem level, it modulates activity in the descending reticular formation, which plays a key role in regulating muscle tone. At the spinal cord level, orphenadrine interferes with interneuronal activity that transmits signals contributing to muscle spasm.
The anticholinergic properties of orphenadrine contribute to its overall pharmacological profile. By blocking muscarinic acetylcholine receptors, it reduces certain types of involuntary muscle activity and may contribute to its analgesic effects. The antihistaminic (H1-blocking) properties also play a role, particularly in producing the sedative effects that some patients experience. These combined mechanisms result in a reduction of painful muscle spasm without causing complete muscle paralysis, allowing patients to continue with rehabilitation activities.
What Should You Know Before Taking Norflex?
Quick Answer: Before taking Norflex, inform your doctor about all medical conditions, especially myasthenia gravis, glaucoma, urinary problems, heart conditions, and gastrointestinal disorders. Do not take Norflex if you are allergic to orphenadrine citrate or any of its ingredients. Avoid use during pregnancy and breastfeeding.
Contraindications
Norflex must not be taken in certain medical situations where the risks of the medication clearly outweigh any potential benefits. The anticholinergic properties of orphenadrine can significantly worsen certain conditions, making it essential to rule out these contraindications before starting treatment. Your doctor will assess your medical history carefully to ensure that Norflex is safe for you.
- Hypersensitivity – Known allergy to orphenadrine citrate or any excipient in the formulation
- Myasthenia gravis – A neuromuscular disease causing muscle weakness; orphenadrine can worsen symptoms
- Urinary obstruction – Including urethral stricture or benign prostatic hyperplasia with urinary retention
- Gastrointestinal obstruction – Including pyloric stenosis or other mechanical obstructions
- Megacolon – Toxic or non-toxic enlargement of the colon
- Narrow-angle glaucoma – The anticholinergic effect can trigger an acute attack by causing pupil dilation
Warnings and Precautions
Even when Norflex is not strictly contraindicated, several conditions require careful monitoring and dose adjustment. The anticholinergic properties of orphenadrine mean that patients with certain cardiovascular, urological, or ophthalmological conditions need particularly close supervision during treatment. Always discuss your full medical history with your prescribing physician.
Patients with cardiac conditions should exercise particular caution. Orphenadrine can cause tachycardia (rapid heart rate), palpitations, and other cardiac rhythm disturbances. Those with pre-existing arrhythmias, angina pectoris, or heart failure should be monitored closely, and the benefits of treatment must be carefully weighed against the cardiovascular risks. In some cases, alternative muscle relaxants without anticholinergic activity may be preferred.
Patients with a shallow anterior eye chamber and narrow chamber angle face a small but serious risk of acute angle-closure glaucoma triggered by pupil dilation (mydriasis) caused by the anticholinergic effects of orphenadrine. While this complication is uncommon, it constitutes a medical emergency requiring immediate treatment. Patients with known risk factors for angle-closure glaucoma should have an ophthalmological assessment before starting Norflex.
Urinary caution is also important. Orphenadrine can reduce detrusor muscle contractility and increase bladder outlet resistance, potentially causing or worsening urinary retention. Men with benign prostatic hyperplasia (BPH) are particularly susceptible to this effect. Patients should report any difficulty urinating, decreased urine flow, or a sensation of incomplete bladder emptying to their doctor promptly.
Pregnancy and Breastfeeding
The use of Norflex during pregnancy is not recommended due to insufficient data on its safety for the developing foetus. Animal reproductive studies are limited, and there are no adequate, well-controlled studies in pregnant women. If you are pregnant, suspect you may be pregnant, or are planning to become pregnant, consult your healthcare provider before taking this medication. Your doctor will assess whether the potential benefits justify the potential risks and may recommend alternative treatments with a better-established safety profile during pregnancy.
It is not known whether orphenadrine is excreted in human breast milk. Due to the potential for adverse effects in the nursing infant – particularly sedation and anticholinergic effects – use during breastfeeding is not recommended. Women who need muscle relaxant therapy while breastfeeding should discuss alternative options with their healthcare provider.
Driving and Operating Machinery
Norflex can impair your ability to drive and operate machinery. The drug commonly causes drowsiness and blurred vision, both of which can significantly affect reaction time and visual acuity. You should assess how Norflex affects you individually before driving or performing any activity that requires alertness and clear vision. It is your responsibility to determine whether you are fit to perform these activities while taking this medication.
How Does Norflex Interact with Other Drugs?
Quick Answer: Norflex interacts with several drug classes including antihistamines, tricyclic antidepressants, MAO inhibitors, opioids, and alcohol. These interactions can increase the risk of anticholinergic side effects, excessive sedation, or respiratory depression. Always inform your doctor about all medications you are taking.
Drug interactions with Norflex are primarily related to its anticholinergic and sedative properties. When combined with other medications that share similar pharmacological effects, the result can be an additive or synergistic increase in side effects. Understanding these interactions is essential for safe use of the medication and for preventing potentially dangerous combinations.
The anticholinergic effects of orphenadrine can be significantly amplified when the drug is combined with other agents possessing anticholinergic activity. This cumulative anticholinergic burden can lead to severe dry mouth, urinary retention, constipation, cognitive impairment, confusion, and in extreme cases, anticholinergic toxicity. Elderly patients are particularly vulnerable to these additive effects and may experience delirium or hallucinations even at standard doses when multiple anticholinergic drugs are combined.
Norflex may also reduce gastrointestinal motility, which can affect the absorption of other orally administered medications. Drugs that rely on consistent gastrointestinal transit times for their absorption may have altered bioavailability when taken concurrently with orphenadrine. This effect is typically most relevant for sustained-release formulations and medications with narrow therapeutic windows.
Major Interactions
| Drug / Drug Class | Type of Interaction | Clinical Significance |
|---|---|---|
| Opioid analgesics (morphine, codeine, tramadol) | Additive CNS depression | Increased risk of drowsiness, respiratory depression, and sedation. Combination requires careful dose adjustment and monitoring. |
| MAO inhibitors (phenelzine, tranylcypromine, selegiline) | Enhanced anticholinergic and sympathomimetic effects | Risk of hypertensive crisis, hyperpyrexia, and severe anticholinergic toxicity. Concurrent use is generally avoided. |
| Tricyclic antidepressants (amitriptyline, nortriptyline) | Additive anticholinergic effects | Significantly increased risk of dry mouth, urinary retention, constipation, confusion, and cognitive impairment. |
| Disopyramide | Additive anticholinergic and cardiac effects | Increased risk of cardiac arrhythmias, urinary retention, and severe anticholinergic toxicity. |
Moderate Interactions
| Drug / Drug Class | Type of Interaction | Clinical Significance |
|---|---|---|
| Antihistamines (diphenhydramine, cetirizine, hydroxyzine) | Additive sedation and anticholinergic effects | Increased drowsiness, impaired coordination, dry mouth. Use first-generation antihistamines with particular caution. |
| Phenothiazines (chlorpromazine, prochlorperazine) | Additive anticholinergic and sedative effects | Increased risk of anticholinergic toxicity, excessive sedation, and extrapyramidal effects. |
| Dopaminergic antiparkinsonian drugs (amantadine, levodopa) | Enhanced anticholinergic effects (especially amantadine) | Amantadine has anticholinergic properties that can combine with orphenadrine. Monitor for confusion, hallucinations, and urinary retention. |
| Alcohol | Reduced efficacy and additive CNS depression | Alcohol may decrease the therapeutic effect of Norflex while simultaneously increasing sedation and impaired coordination. |
| Other antispasmodics (hyoscine, propantheline) | Additive anticholinergic effects | Cumulative anticholinergic burden increases risk of dry mouth, constipation, urinary retention, and cognitive effects. |
What Is the Correct Dosage of Norflex?
Quick Answer: The usual adult dose of Norflex is one 100 mg extended-release tablet taken twice daily, in the morning and evening. The extended-release tablet must be swallowed whole – never crushed, chewed, or broken. Your doctor will determine the optimal dose for your individual needs.
Norflex is formulated as an extended-release (sustained-release) tablet designed to deliver the active ingredient gradually over approximately 12 hours. This controlled-release mechanism is critical to maintaining consistent therapeutic drug levels while minimising peak-related side effects. The integrity of the tablet coating must be preserved for the extended-release system to function correctly.
Adults
Standard Adult Dosage
Dose: 100 mg (one extended-release tablet) twice daily
Timing: Morning and evening, approximately 12 hours apart
Administration: Swallow whole with a full glass of water. Do not crush, chew, or split the tablet.
Duration: As directed by your physician. Typically used for short-term treatment of acute musculoskeletal conditions.
The prescribing physician will determine the appropriate dose based on individual patient factors including the severity of symptoms, response to treatment, and tolerance of the medication. Some patients may require dose adjustments based on their clinical response, particularly those with impaired hepatic function, as orphenadrine is extensively metabolised by the liver.
Elderly Patients
Elderly patients may be more sensitive to the anticholinergic and sedative effects of Norflex. These patients are at higher risk of confusion, hallucinations, urinary retention, constipation, and falls related to dizziness and sedation. Healthcare providers should exercise caution when prescribing Norflex to elderly patients and may consider lower doses or shorter treatment durations. The Beers Criteria, a widely used reference for potentially inappropriate medications in older adults, includes anticholinergic muscle relaxants as drugs to be used with caution in this population.
Children
The safety and efficacy of Norflex in children have not been established. Norflex is not recommended for use in paediatric patients. If a child is experiencing musculoskeletal pain, the treating physician should consider age-appropriate alternative treatments including physiotherapy, rest, and other analgesic medications with established paediatric safety profiles.
Missed Dose
If you forget to take a dose of Norflex, take it as soon as you remember unless it is nearly time for your next scheduled dose. In that case, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a forgotten tablet, as this increases the risk of side effects including excessive drowsiness, dry mouth, and urinary retention.
Overdose
If you have taken more Norflex than prescribed, or if a child has accidentally ingested the medication, seek immediate medical attention or contact your local poison control centre. Orphenadrine overdose can be serious and potentially life-threatening.
Symptoms of overdose may include:
- Restlessness and agitation
- Dilated pupils (mydriasis)
- Low blood pressure (hypotension)
- Slow or irregular heartbeat (bradycardia or arrhythmias)
- Seizures (convulsions)
- Respiratory depression
Treatment of overdose is supportive and symptomatic, typically requiring hospitalisation for cardiac monitoring and management of complications.
What Are the Side Effects of Norflex?
Quick Answer: Common side effects of Norflex include drowsiness, blurred vision, and dry mouth. Very rare side effects include accommodation difficulties. Reported but uncommon effects include hallucinations, confusion, tremor, palpitations, nausea, constipation, and urinary difficulties. Most side effects are related to the anticholinergic properties of the drug.
Like all medicines, Norflex can cause side effects, although not everyone will experience them. The side effects of orphenadrine are primarily related to its anticholinergic and central nervous system-depressant properties. Most side effects are mild to moderate in severity and tend to diminish as the body adjusts to the medication over the first few days of treatment. However, some patients may find certain effects particularly troublesome or persistent, warranting discussion with their prescribing physician.
The anticholinergic effects of Norflex – such as dry mouth, blurred vision, and urinary difficulties – are dose-dependent, meaning they are more likely and more pronounced at higher doses. Elderly patients are generally more susceptible to these effects due to age-related changes in drug metabolism and increased sensitivity to anticholinergic medications. Patients should report any new or worsening symptoms to their healthcare provider, as dose adjustment or discontinuation may be necessary.
Common
May affect up to 1 in 10 people
- Drowsiness and fatigue
- Blurred vision
- Dry mouth (xerostomia)
Very Rare
May affect up to 1 in 10,000 people
- Difficulty with visual accommodation (cycloplegia)
Not Known
Frequency cannot be estimated from available data
- Hallucinations
- Confusion and disorientation
- Tremor
- Dizziness
- Palpitations (awareness of heartbeat)
- Nausea
- Constipation
- Difficulty urinating (urinary hesitancy or retention)
When to Seek Medical Attention
While most side effects of Norflex are mild and self-limiting, certain symptoms require prompt medical evaluation. You should contact your doctor immediately if you experience severe confusion or hallucinations, significant difficulty urinating or complete inability to pass urine, rapid or irregular heartbeat, severe eye pain (which could indicate acute angle-closure glaucoma), or any signs of a severe allergic reaction such as swelling of the face, lips, tongue, or throat, difficulty breathing, or widespread skin rash.
How Should You Store Norflex?
Quick Answer: Store Norflex at room temperature, away from moisture and direct sunlight. Keep the medication out of the sight and reach of children. Do not use after the expiry date printed on the packaging.
Proper storage of medications is essential to maintain their efficacy and safety throughout the treatment period. Norflex extended-release tablets should be stored under standard conditions to preserve the integrity of the formulation, particularly the extended-release coating that controls drug delivery.
Keep Norflex in its original blister packaging until use. Store the tablets at room temperature (below 25°C / 77°F) in a dry place, protected from excessive heat, moisture, and direct sunlight. Do not store the medication in bathrooms or near kitchen sinks where humidity levels fluctuate. Ensure the medication is stored securely out of the sight and reach of children, as accidental ingestion by a child could be dangerous.
Do not use Norflex after the expiry date stated on the carton and blister pack. The expiry date refers to the last day of the indicated month. Expired medications may have reduced efficacy and could potentially be harmful. Do not dispose of medications via household waste or wastewater. Ask your pharmacist about appropriate disposal methods for medicines that are no longer needed, as proper disposal helps protect the environment.
What Does Norflex Contain?
Quick Answer: Norflex contains the active substance orphenadrine citrate (100 mg per extended-release tablet). Inactive ingredients include lactose monohydrate, acacia, ethylcellulose, magnesium stearate, and colloidal silicon dioxide.
Understanding the full composition of a medication is important for identifying potential allergens and understanding how the drug is formulated. The composition of Norflex has been carefully designed to provide a controlled-release formulation that delivers the active ingredient steadily over 12 hours.
Active Ingredient
Each extended-release tablet contains 100 mg of orphenadrine citrate as the active pharmaceutical ingredient. Orphenadrine citrate is the citrate salt form of orphenadrine, which improves the compound's water solubility and bioavailability compared to the free base. The molecular formula is C18H23NO · C6H8O7.
Inactive Ingredients (Excipients)
The following excipients are used in the manufacture of Norflex extended-release tablets, each serving a specific function in the formulation:
- Lactose monohydrate – A sugar-based filler and binder that provides bulk and structural integrity to the tablet
- Acacia (gum arabic) – A natural polysaccharide used as a binding agent and to assist with the extended-release properties
- Ethylcellulose – A semisynthetic polymer that forms the primary extended-release coating, controlling the rate of drug release
- Magnesium stearate – A lubricant that prevents the tablet from sticking to manufacturing equipment during the compression process
- Colloidal silicon dioxide – A flow agent (glidant) that ensures uniform powder distribution during tablet manufacturing
Pack Size
Norflex is available in blister packs containing 60 extended-release tablets. The blister packaging protects the tablets from moisture and physical damage, helping to maintain the integrity of the extended-release coating.
Frequently Asked Questions About Norflex
Norflex (orphenadrine citrate) is a muscle relaxant prescribed to relieve muscle pain and discomfort associated with acute musculoskeletal conditions. Common uses include muscle strains, acute lower back pain (lumbago), skeletal injuries, and neck pain from whiplash or torticollis. It works by acting on the central nervous system to reduce muscle spasm and also has mild pain-relieving properties.
The most common side effects of Norflex are drowsiness, blurred vision, and dry mouth. These effects are related to the drug's anticholinergic properties and typically affect up to 1 in 10 people. Most side effects are mild and tend to diminish as your body adjusts to the medication. If any side effect becomes bothersome or persistent, consult your doctor about possible dose adjustments.
Alcohol consumption while taking Norflex is not recommended. Alcohol can decrease the therapeutic effectiveness of Norflex while simultaneously increasing sedative side effects such as drowsiness, dizziness, and impaired coordination. This combination can significantly impair your ability to drive or operate machinery and increases the risk of falls and accidents. If you consume alcohol regularly, discuss this with your doctor before starting Norflex.
No, Norflex extended-release tablets must be swallowed whole. Crushing, chewing, or splitting the tablet destroys the extended-release mechanism, which could cause too much of the active ingredient to be released at once. This can lead to a higher peak blood concentration, increasing the risk of side effects while reducing the duration of therapeutic effect. If you have difficulty swallowing tablets, discuss alternative formulations or medications with your doctor.
Elderly patients are generally more sensitive to the anticholinergic effects of Norflex, including confusion, drowsiness, urinary retention, and constipation. The American Geriatrics Society Beers Criteria identifies anticholinergic muscle relaxants as potentially inappropriate for older adults due to these risks. If Norflex is prescribed to an elderly patient, the doctor should use the lowest effective dose, monitor closely for side effects, and limit the duration of treatment. Falls risk is also a concern due to drowsiness and dizziness.
Norflex extended-release tablets are designed to release the active ingredient gradually. Most patients begin to notice some relief of muscle pain and spasm within 1 to 2 hours of taking the first dose, with peak effects occurring at approximately 6 to 8 hours. The extended-release formulation provides sustained therapeutic levels for approximately 12 hours, which is why the medication is taken twice daily. Full therapeutic benefit for some conditions may take several days of consistent use.
References
- World Health Organization (WHO). WHO Model List of Essential Medicines – 23rd List. Geneva: WHO; 2023. Available at: who.int/publications
- European Medicines Agency (EMA). Summary of Product Characteristics: Orphenadrine Citrate Extended-Release Tablets. EMA; 2024.
- British National Formulary (BNF). Orphenadrine Citrate. NICE; 2025. Available at: bnf.nice.org.uk
- van Tulder MW, Touray T, Furlan AD, Solway S, Bouter LM; Cochrane Back Review Group. Muscle relaxants for nonspecific low back pain: a systematic review within the framework of the Cochrane Collaboration. Spine. 2003;28(17):1978-1992. doi:10.1097/01.BRS.0000090503.38830.AD
- Chou R, Peterson K, Helfand M. Comparative efficacy and safety of skeletal muscle relaxants for spasticity and musculoskeletal conditions: a systematic review. J Pain Symptom Manage. 2004;28(2):140-175. doi:10.1016/j.jpainsymman.2004.05.002
- American Geriatrics Society Beers Criteria Update Expert Panel. American Geriatrics Society 2023 Updated AGS Beers Criteria for Potentially Inappropriate Medication Use in Older Adults. J Am Geriatr Soc. 2023;71(7):2052-2081.
- Toth PP, Urtis J. Commonly used muscle relaxant therapies for acute low back pain: a review of carisoprodol, cyclobenzaprine hydrochloride, and metaxalone. Clin Ther. 2004;26(9):1355-1367.
- U.S. Food and Drug Administration (FDA). Orphenadrine Citrate – Prescribing Information. FDA; 2024. Available at: fda.gov
Editorial Team
This article was written by the iMedic Medical Editorial Team, a group of licensed physicians specialising in musculoskeletal medicine, clinical pharmacology, and pain management. All content is reviewed according to international medical standards and evidence-based guidelines.