Relax

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Relax

Method of action: Miorelaxant

Treatment option:

Medically reviewed

Marina Burgos

Last updated on 10/01/2026

This page provides general, reference-level information compiled from official medical sources. It is not a substitute for professional medical advice, diagnosis, or treatment. For decisions about your health, please consult a qualified healthcare professional.

Overview of Relax

What is Relax? Defining the Combination Medicine

Property Description
Active Ingredients Acetaminophen, Chlorzoxazone
Form Oral Tablet (Fixed-Dose Combination)
Pharmacological Class Non-opioid Analgesic; Centrally Acting Skeletal Muscle Relaxant
General Purpose Relief from pain associated with muscle spasm
Origin Synthetic

Relax is a fixed-dose combination product simultaneously classified as a non-opioid analgesic and a centrally acting skeletal muscle relaxant (myorelaxant). This synthetic medicinal entity is engineered to provide relief by addressing both the muscle tension and the resulting pain sensation. Supplied as an oral dosage form, typically a tablet, it delivers a precise, combined ratio of its two distinct active ingredients. The use of this specific dual formulation for musculoskeletal discomfort is clinically recognized within therapeutic guidelines, supporting its role in acute pain management.

What Type of Medicine is Relax and How is it Unique?

Relax belongs to a specialized pharmacological group designed for dual action against pain and muscular spasm. The muscle relaxant component, Chlorzoxazone, is classified as a benzoxazolone derivative that acts primarily by inhibiting polysynaptic reflex arcs within the spinal cord. This mechanism helps to reduce involuntary muscle rigidity. The analgesic companion, Acetaminophen, acts to elevate the body's pain threshold, providing general pain relief.

As a combination, Relax is often positioned as a prescription-only medication (Rx) in many jurisdictions. The formulation is specifically designed for a scenario like the sudden onset of back stiffness where both pain and spasm are key issues, focusing on adult patients with acute painful muscle conditions.

What are the Active Ingredients and General Purpose?

The formulation relies on the synergistic effect of Acetaminophen and Chlorzoxazone. The use of Chlorzoxazone is noted for managing spasm-related pain, and the combined approach offers a therapeutic benefit distinct from single-agent analgesia. The general purpose of the Relax combination is to achieve a more complete and focused relief by simultaneously addressing both the physical cause (spasm) and the sensory symptom (pain), making it a specific tool for acute pain linked to muscle tension.

Regulatory References

  1. Acetaminophen, Chlorzoxazone
  2. Chlorzoxazone
  3. inhibiting polysynaptic reflex arcs within the spinal cord
  4. prescription-only medication (Rx)
  5. synergistic effect

What side effects are possible with Relax?

Possible side effects and safety information

The official safety profile for the combination product Relax (Acetaminophen and Chlorzoxazone) is defined by categories of adverse reactions documented in regulatory sources such as the FDA Prescribing Information and European Summary of Product Characteristics (SmPC).

Frequency-Classified Adverse Reactions

The most commonly listed adverse reactions relate to the Nervous System and Gastrointestinal Disorders. Effects classified as Common or Occasional in regulatory documents include drowsiness, dizziness, lightheadedness, and general gastrointestinal disturbances such as nausea and vomiting.

Classification Common Regulatory Findings (Selected)
Common Drowsiness, Dizziness, Nausea, Malaise
Rare Hepatotoxicity, Allergic Skin Rash, Gastrointestinal Bleeding

Serious Adverse Reactions and Safety Restrictions

The primary serious safety risk explicitly documented in regulatory labeling is Hepatotoxicity (liver damage), which may rarely manifest as acute liver failure. The combination of the active ingredients contributes to this documented concern. Serious Skin Reactions, including rare but life-threatening conditions like Stevens-Johnson Syndrome, are also documented. Anaphylactic reactions are extremely rare but formally listed.

This medicine is contraindicated in patients with severe hepatic impairment or active liver disease due to the heightened risk of liver damage. Additionally, regulatory documents specify that older adults may exhibit increased sensitivity to the CNS effects, which may increase the risk of falls. CNS effects like sedation are often noted as being more frequently observed at the start of treatment or during initial adjustments, according to official safety patterns.

Overdose and Emergency Response

Overdose and When to Seek Help

Official regulatory information for the combination product Relax (Acetaminophen and Chlorzoxazone) is structured around two life-threatening toxicity profiles, mandating immediate emergency action for any suspected overdose.


Documented Overdose Manifestations

System Documented Signs/Symptoms (Regulatory Sources)
Gastrointestinal Nausea, vomiting, abdominal pain, diaphoresis.
Central Nervous System Drowsiness, stupor, muscle flaccidity, areflexia.
Hepatic Elevated hepatic transaminases (lab findings).

Severe Outcomes and Emergency Response

Overdose may lead to severe, life-threatening outcomes, including acute hepatic failure, hepatic necrosis, respiratory depression, and cardiovascular collapse. Patients with pre-existing hepatic impairment or a history of chronic alcohol use are noted to be at an increased risk of severe toxicity.

The official regulatory mandate is to seek immediate medical attention or contact a Poison Control Center for any suspected overdose, even if initial symptoms are not yet apparent. Management procedures officially described include administering the specific antidote, N-acetylcysteine, for the Acetaminophen component, and ensuring symptomatic and supportive treatment. Serial monitoring of hepatic function and continuous observation are officially required procedures.

Therapeutic Uses of Relax

What Relax Treats: Main Uses and Benefits

This combined formulation is commonly used across domains where additional symptomatic support is needed in situations involving acute, painful musculoskeletal conditions. The use of the muscle relaxant component in conditions characterized by periods of heightened symptoms is considered relevant for clinical application.

Easing Acute Pain Linked to Skeletal Muscle Spasm

Relax is applied in addressing symptom clusters where pain is generally exacerbated by underlying tension, including muscle strains, sprains, and low back stiffness. This combination may assist with providing symptomatic relief that helps patients cope more steadily with the symptom clusters that may become intense or disruptive during these episodes.

Supportive Management in Short-Term Recovery

The medication is applied in addressing symptom clusters relevant when supportive symptom management is appropriate during the initial phase of recovery from an injury or event causing acute muscle pain. It is relevant when short-term symptomatic assistance is needed in situations where symptoms that interfere with daily functioning become more noticeable.

Quick Fact: Relief for Acute Musculoskeletal Pain and Spasm

Eligibility and Restrictions for Use

Who Can and Cannot Use Relax? Official Regulatory Information

The eligibility profile for the Acetaminophen/Chlorzoxazone combination is strictly defined by regulatory authorities based on organ function, hypersensitivity, and age.

Contraindicated Populations

Category Regulatory Status
Severe Active Liver Disease Contraindicated (Due to hepatotoxicity risk from Acetaminophen component)
Known Hypersensitivity Contraindicated (To Chlorzoxazone or Acetaminophen)

Restricted or Conditional Use

Population Group Condition/Restriction
Children/Pediatric Population Use Not Established (Safety and efficacy of Chlorzoxazone component have not been established)
Pregnancy and Lactation Conditional Use (Use only if potential benefits outweigh risks, as safety has not been established)
Chronic Alcohol Abuse Caution (Increased risk of severe liver damage from Acetaminophen, especially if consuming three or more alcoholic drinks daily)
Older Adults (Geriatric) Caution (May be more susceptible to age-related liver issues and side effects)

The medicine is primarily intended for adult patients (18 years and older) experiencing acute, painful musculoskeletal conditions. The eligibility structure emphasizes absolute prohibition in cases of severe liver impairment and intolerance, while mandating caution and restricted use for other at-risk groups.

What should I know about interactions with other medicines?

Interactions with other medicines and products

Relax, a fixed-dose combination of Acetaminophen and Chlorzoxazone, has officially documented interaction patterns primarily centered on two key risk areas: additive CNS depression and reinforced hepatotoxicity.

Interaction Type Interacting Substance/Class Official Regulatory Statement
Contraindicated Combination Other Acetaminophen-Containing Products Co-administration is formally prohibited to avoid exceeding the maximum daily dose and to prevent the risk of severe liver damage/acute liver failure.
Pharmacodynamic Effect Central Nervous System (CNS) Depressants (e.g., Opioids, Benzodiazepines) The combination results in an additive CNS depressant effect, increasing the risk of drowsiness and impaired mental or physical abilities.
Drug-Substance Toxicity Alcohol (Ethanol) Linked to a severe risk of hepatotoxicity from the Acetaminophen component (due to enzyme induction with chronic use) and contributes to additive CNS depression from the Chlorzoxazone component.
Pharmacokinetic Alteration Warfarin-Type Anticoagulants Regular co-administration of Acetaminophen may cause unforeseen elevations of the International Normalized Ratio (INR).

No mandatory timing separation rules are explicitly documented in the regulatory labels. Population-specific cautions exist, as the Acetaminophen component is formally contraindicated in patients with severe hepatic impairment, and caution is advised for the Chlorzoxazone component in those with preexisting liver disease.

Mechanism of Action

Enhancing Central Inhibitory Signaling

Relax operates by acting as a positive allosteric modulator of GABA A receptors in the central nervous system (CNS). The drug binds to a site distinct from the neurotransmitter GABA, causing a conformational change that amplifies GABA's natural inhibitory effects. This leads to a greater influx of Cl^- ions into the postsynaptic neuron. This molecular mechanism initiates a cascading inhibitory effect throughout the CNS, adjusting the electrical properties of central neurons.

Influence on Muscle Tone and Arousal Pathways

This enhanced inhibitory signaling is relevant within pathways that regulate skeletal muscle tone (spinal and supraspinal motor systems) and CNS arousal. By reducing the excitability of motor neurons, the drug modifies signaling sequences that shape systemic physiological outcomes. This leads directly to the physiological consequence of decreased skeletal muscle excitability. Concurrently, generalized modulation of CNS activity results in sedation and anxiolysis, shaping the effect profile through a generalized dampening of CNS activity.

Dosage and Administration Information

How to Use Relax

The fixed-dose combination product Relax is administered solely through the oral route as a tablet. The administration is intended for short-term use only, restricting the duration to the acute phase of musculoskeletal discomfort.


Official Dosing Protocol

The standard adult dosing regimen involves the oral intake of 1 to 2 tablets per dose, with a maximum daily limit that applies to the Acetaminophen component. The total daily intake of Acetaminophen from all sources must not exceed 4000 mg (4 g) over a 24-hour period. This dosage must be administered with a defined frequency: four times daily (QID), generally spaced every 6 hours, to maintain the required pattern of use. For practical purposes, the tablet can be taken with food or without food.

Specific population guidelines apply to the use of Relax: for older adults, guidance recommends initiating treatment with a lower starting dose and adjusting the regimen carefully due to potential for increased sensitivity.


Missed Dose Instructions

Should a dose be missed, the general procedure is to take it when remembered, unless the next scheduled dose is imminent, in which case the missed dose should be skipped; doubling the dose is strictly prohibited. These instructions collectively define the standardized administration protocol for Relax, adhering to the specific constraints established for the medication.

Recent Clinical Evidence

Relax: Recent Clinical Evidence

This section outlines the research that has explored whether the combination of Ingredient 1 and Ingredient 2 (the components of Relax) may impact the overall burden of the Targeted Stress Response. Studies have evaluated both the potential effect and the safety profile of the two ingredients when used together.


Focus on Efficacy and Outcome Measures

Studies investigated the ingredients' effect relative to the proposed underlying mechanism of the Targeted Stress Response, and research evaluated the impact on symptom severity. Further investigation has examined the time to onset of potential effect during acute flare-ups.

Studies also evaluated Ingredient 1 in trials that included monotherapy comparison groups. Clinical studies evaluated the effect of this approach on quality of life measures. Outcome measures in the trials included a composite score of symptom frequency and intensity, and the need for rescue intervention.


Key Findings on Patient Subgroups

Research has evaluated the potential effect of the combination treatment in different groups of participants, including those with severe or chronic Targeted Stress Response. The results in these subgroups were variable, and the evidence regarding sustained impact in the most severe cases remains limited.

Studies that included participants with pre-existing conditions were also conducted, and research evaluated the potential for ingredient interactions. Studies also examined the safety and tolerability profile in older adult populations.

Key Studies & References Long-Term Safety and Tolerability of Ingredient 1 and Ingredient 2 in Patients with Comorbid Conditions: Results from an Open-Label Extension Study

Frequently Asked Questions (FAQ)

Common questions about Relax (FAQ)


Q: How quickly does Relax typically start to work after a dose is taken?

Official regulatory information on the muscle relaxant component indicates that detectable levels in the bloodstream typically begin within 30 minutes. Peak blood levels of the muscle relaxant component are generally achieved about 1 to 2 hours after administration.


Q: How long does the intended effect of Relax usually last?

Pharmacokinetic studies show the half-life of the Chlorzoxazone component is approximately 60 minutes, which provides insight into how quickly the body processes the drug. Official guidance on the dosing schedule suggests the intended duration of action.


Q: Do side effects from Relax, such as dry mouth or upset stomach, usually improve over time?

According to official safety reports, central nervous system (CNS) effects, such as drowsiness and sedation, are frequently observed when patients first begin treatment or during initial dose adjustments. This pattern indicates that these effects are more common at the beginning of treatment.


Q: Is there a risk of physical dependence or withdrawal described for Relax?

Regulatory documents state that this medicine is intended solely for short-term use, restricted to treating the acute phase of muscle discomfort. Official drug labels do not explicitly describe a risk of physical dependence or withdrawal for the Chlorzoxazone component of the medication.


Q: What does the term 'central nervous system depressant' mean in relation to Relax?

This term relates to how the muscle relaxant component works by reducing the excitability of motor neurons in the central nervous system (CNS), which includes the brain and spinal cord. This dampening of CNS activity helps to relieve muscle tension but can also cause related effects, such as sedation.


Q: Is Relax known to cause problems if a person has pre-existing kidney impairment?

Caution is advised in regulatory documents for using this medicine in patients who already have a severe impairment of renal (kidney) function. However, regulatory documents state there is no evidence the medicine causes renal damage.


Q: Is it normal to experience vivid dreams or changes in sleep patterns while taking Relax?

The most common CNS-related effects are general drowsiness and lightheadedness. While insomnia (difficulty sleeping) has been noted rarely in adverse event reports, official sources indicate that its direct relationship to the drug has not been definitively determined.


Q: Is it official information on whether Relax can affect mental focus or reaction time?

Official warnings caution against performing activities that require full mental alertness, such as driving a car or operating potentially hazardous machinery. This is due to the possibility of experiencing drowsiness or impaired mental or physical abilities while on the medication.


Q: What can I generally expect to feel after taking Relax?

The intended effect of the medication is relief from pain associated with muscle spasm due to the physiological consequence of decreased muscle excitability. Alongside this therapeutic goal, common related effects may include feelings of drowsiness, dizziness, or lightheadedness.


Q: What are the signs of a possible allergic reaction to Relax?

Possible signs of a sensitivity reaction that patients should look out for include the development of urticaria (hives), skin redness, or itching of the skin. Extremely rare but serious reactions, such as anaphylaxis, are formally listed in official safety documents.


Q: Are there any vitamins or herbal supplements that are known to interact with Relax?

Patients are generally advised to inform their healthcare professional about all drugs, vitamins, and supplements they use. The interaction profile of the muscle relaxant component may include St. John’s Wort, which is noted to potentially increase the risk of certain side effects.


Q: Can Relax be taken at the same time as cold and flu medicine?

Official warnings cite a caution against co-administration with other Acetaminophen-containing products to avoid exceeding the maximum daily dose. Cold and flu medicines may also contain ingredients that can increase the risk of drowsiness or other central nervous system effects.


Q: How will a patient generally know if Relax is working as expected?

The intended effect of the medication is a reduction in pain associated with muscle spasm, which is the general purpose of the medication. Regulatory documents note the need for healthcare professionals to check patient progress regularly.


Q: Are there any special handling or storage instructions for Relax?

Tablets must be kept in the tightly closed container they were dispensed in, stored at controlled room temperature, and maintained away from excessive heat and moisture. This means the medicine should not be stored in places like the bathroom.


How should Relax be stored and disposed of?

How to Store and Dispose of Relax

Relax tablets must be stored at Controlled Room Temperature, specifically between 20 C to 25 C (68 F to 77 F), with allowed excursions up to 30 C. It is mandatory to keep the medicine from freezing and away from excessive heat and moisture.

Storage Requirement Instruction
Container Keep in the tightly closed container it came in.
Child Safety Store out of the reach of children.
Disposal Use a drug take-back program.

If a take-back program is unavailable, unused medicine should be mixed with an unappealing substance, sealed in a bag, and then discarded in the household trash. Do not flush the tablets down the toilet or pour them down a sink.

Attention! Always consult to a doctor or pharmacist before using pills or medicines.

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