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Methocarbamol (Robaxin) Uses & Side Effects

Written by Mathew Eng, PharmD | Last updated:
Jonathan Ritter
Puya Yazdi
Medically reviewed by
Jonathan Ritter, PharmD, PhD (Pharmacology), Puya Yazdi, MD | Written by Mathew Eng, PharmD | Last updated:

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Muscle pain (such as lower back pain) and muscle spasms are very common problems, affecting millions of people. Muscle spasms and pain are often treated with muscle relaxants, such as methocarbamol, which repress the nervous system to provide temporary relief. Read on to learn more about the uses and side effects of methocarbamol.

What is Methocarbamol?

Methocarbamol (brand name Robaxin) is a prescription medication used to treat muscle spasms and pain. This drug is typically used in combination with physical therapy, rest, and other treatments to provide short-term pain relief from painful muscular conditions [1].

Mechanism of Action

The mechanism of action of methocarbamol is not fully understood.

Research suggests that methocarbamol primarily works by suppressing the nervous system by blocking nerve signals from the spine. It may also block acetylcholinesterase, an enzyme that breaks down the neurotransmitter acetylcholine, which plays an important role in muscle activation [1, 2, 3].

Although it is referred to as a muscle relaxant, methocarbamol doesn’t appear to directly affect muscle contraction. However, methocarbamol may increase the refractory period of muscles, which is the period of time that the muscle is relaxed and unable to respond to signals from the nerves [4, 2].

Uses of Methocarbamol

Muscle Spasms and Pain

Methocarbamol is FDA-approved to treat pain from musculoskeletal conditions. Musculoskeletal conditions include disorders that may affect the joints, bones, muscles, tendons, ligaments, and nerves [5].

Methocarbamol is typically not used alone. Instead, it should be used in combination with other treatments, physical therapy, and/or rest [6].

Despite the relatively widespread use of methocarbamol for a variety of painful muscle conditions, there is limited clinical research for this use [7].

An older randomized placebo-controlled trial of 59 patients with painful muscle spasm found that methocarbamol was effective in 60% of the patients. However, 30% of the patients that took the placebo also reported symptom relief [8].

According to a multi-center randomized placebo-controlled trial of 202 patients with lower back pain, methocarbamol may reduce pain and improve mobility [9].

Another randomized placebo-controlled trial of 100 patients who suffered from muscle cramps due to liver disease found that methocarbamol may reduce the frequency and duration of cramps [10].

In a retrospective cohort study including 592 patients who sustained closed rib fractures, methocarbamol was associated with shorter lengths of hospital stay [11].

However, a systematic review of 101 clinical trials that examined various muscle relaxant drugs concluded that the clinical research on methocarbamol is very limited and there is insufficient evidence to determine its effectiveness or safety [7].

Safety of Methocarbamol

Side Effects

Methocarbamol can cause several side effects. If any side effects persist or worsen, let your doctor know. This is also not a complete list of possible side effects. Tell your doctor if you experience any serious side effects or notice any effects not listed here.

Some common side effects include [6]:

  • Nausea
  • Vomiting
  • Upset stomach
  • Drowsiness
  • Dizziness

Some serious side effects include [6]:

  • Trouble breathing
  • Severe dizziness
  • Swelling of the face, tongue, or throat
  • Persistent nausea or vomiting

Warnings

Drowsiness and Dizziness

Methocarbamol works by suppressing the nervous system, which may cause significant drowsiness or dizziness. Those taking methocarbamol should not operate a motor vehicle or machinery until they know how this medication affects them [6].

Methocarbamol should not be taken with other substances that can depress the nervous system, such as other muscle relaxants or alcohol.

Interactions with Laboratory Tests

There’s some evidence that methocarbamol may interfere with certain lab tests. Always let your medical team know about all the medications you are taking to avoid any unwanted interactions.

For example, there is a case report of methocarbamol causing a false-positive result on a vanillylmandelic acid (VMA) excretion test, which is used to help diagnose specific types of cancer. However, this type of test is not commonly used anymore [12, 13].

There is another case report of methocarbamol causing a false-positive result on a 5-hydroxyindoleacetic acid (5-HIAA) excretion test, which is also used to help diagnose certain cancers [14, 15].

Risk of Injury in the Elderly

Methocarbamol and other muscle relaxants should be used with caution in the elderly because of an increased risk of falls and injury [16, 17].

Contraindications

People who are allergic or hypersensitive to methocarbamol or any of its components should not take this medication [6].

Pregnancy and Breastfeeding

There is some evidence that methocarbamol may cause birth defects when used during pregnancy. Women who are pregnant or plan to become pregnant should not use methocarbamol unless a doctor determines that the benefits outweigh the possible risks [6].

It’s unclear if meloxicam is present in breast milk. A doctor will weigh the benefits and risks when determining if the use of meloxicam is appropriate during breastfeeding.

Drug Interactions

The following drugs have been reported to interact with methocarbamol. However, this is not a complete list, let your doctor know of all the medications you are currently taking to avoid any unexpected interactions.

  • Other muscle relaxants, such as tizanidine, carisoprodol, cyclobenzaprine
  • Opioid medications, such as morphine, oxycodone, hydrocodone
  • Barbiturate medications, such as phenobarbital and secobarbital
  • Benzodiazepines, such as lorazepam, clonazepam, and diazepam
  • Pyridostigmine bromide

Is Methocarbamol a Narcotic?

With all muscle relaxants, there is some potential for drug abuse. Methocarbamol has sedative effects and may cause dysphoria had higher doses [18].

However, there is some evidence that the potential for abuse of methocarbamol may be lower than similar drugs, such as carisoprodol. One study suggests that the abuse potential of methocarbamol is similar to lorazepam. Always use the lowest effective dose to minimize the potential for abuse [18, 19].

Methocarbamol Dosage and Forms

The dosing of meloxicam can vary. Always take this medication as directed by a doctor.

Methocarbamol is available as an oral tablet and as an injection.

Oral tablets are available in strengths of 500 mg and 750 mg.

The initial dosage of oral methocarbamol is usually 1,500 mg taken 4 times a day.

The maintenance dosage is usually 1,000 mg taken 4 times a day or 750 mg taken every 4 hours.

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About the Author

Mathew Eng

Mathew Eng

PharmD
Mathew received his PharmD from the University of Hawaii and an undergraduate degree in Biology from the University of Washington.
Mathew is a licensed pharmacist with clinical experience in oncology, infectious disease, and diabetes management. He has a passion for personalized patient care and believes that education is essential to living a healthy life. His goal is to motivate individuals to find ways to manage their chronic conditions.

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