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Rx pill bottle: Methocarbamol side effects and how to avoid them
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Methocarbamol side effects and how to avoid them

Methocarbamol side effects include weight gain, constipation, dry mouth, headache, and itching
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By | Aug. 18, 2022 Medically reviewed by Anne Jacobson, MD, MPH

Common methocarbamol side effects | Serious side effects | Weight gain | Constipation | Dry mouth | Headache | Itching | Side effects timeline | Contraindications | Warnings | Interactions | How to avoid side effects | How to treat side effects

Methocarbamol is a prescription muscle relaxant. It is used to relieve muscle pain, spasms, and rigidity. As a sedative, methocarbamol slows down the central nervous system, but it does not directly affect the ability of muscles to contract. Methocarbamol can be given as a tablet or an injection. Robaxin is a brand-name version of methocarbamol injection. Many side effects, like drowsiness and dizziness, are related to the sedative effects of methocarbamol. Even if not entirely avoidable, these problems can usually be managed.

Common side effects of methocarbamol

Common side effects of methocarbamol include dizziness and sleepiness. About 1 in 10 people will have problems with one or the other. The most common side effects are:

  • Sleepiness
  • Dizziness
  • Nausea
  • Indigestion
  • Metallic taste in the mouth
  • Flushing
  • Fainting
  • Hives
  • Itching
  • Skin rash
  • Vertigo
  • Headache
  • Insomnia
  • Vomiting
  • Double vision
  • Blurred vision
  • Fever
  • Stuffy nose
  • Conjunctivitis
  • Low blood pressure

Pain, redness, or itching may occur at the injection site for people who take methocarbamol by injection.

Serious side effects of methocarbamol

More serious side effects of methocarbamol may include:

  • Fainting
  • Seizures
  • Slow heartbeat
  • Severe allergic reactions
  • Low blood counts
  • Confusion and forgetfulness
  • Jaundice

Methocarbamol given in an IV has been known to cause convulsive seizures in people who have a seizure disorder. Additionally, the injected drug sometimes leaks into the surrounding skin, causing redness, pain, tissue death, and skin shedding. 

Weight gain

Weight gain or weight loss are not side effects of methocarbamol. Skeletal muscle relaxants don’t affect weight. If weight gain is an issue while taking methocarbamol, it may be due to reduced mobility and exercise from the underlying condition.

Constipation

Methocarbamol is not associated with constipation or diarrhea. Some other muscle relaxants such as orphenadrine or Fexmid (cyclobenzaprine) may cause constipation. Like many prescription drugs, methocarbamol may cause nausea, vomiting, or stomach upset. 

Dry mouth

Dry mouth is not a side effect of methocarbamol. However, other muscle relaxants, such as Fexmid (cyclobenzaprine) and Zanaflex (tizanidine), do cause dry mouth. 

Headache

Headache is a side effect of methocarbamol, but the incidence is unknown. If headaches are a problem, ask the prescribing healthcare provider for medical advice on how to handle them.

Itching

Skin reactions such as itching, hives, and skin rash may occur with methocarbamol, but their incidence hasn’t been determined. These reactions may be simply a bother, but they may also be a sign of an allergy to the medication. If itching or skin rash, especially hives, occur when taking methocarbamol, contact a healthcare professional.

How soon do methocarbamol side effects start?

Once a tablet is swallowed, methocarbamol hits its maximum concentration in the body in about one hour. Many common side effects, especially sleepiness, dizziness, and lightheadedness, will be experienced soon after taking the medication. A few side effects, such as seizures or jaundice, may take a few days or weeks of treatment to become a problem. People receiving methocarbamol in an IV may start feeling side effects right away. These may include serious side effects such as seizures, slowed heart rate, fainting, and low blood pressure.

How long do methocarbamol side effects last?

Most common side effects of methocarbamol clear up when the drug is eliminated from the body. That doesn’t take long. After the last dose, it should take about five hours or so. A few effects may take longer to resolve, such as any falls or injuries sustained while feeling lightheaded.

What are the long-term side effects of methocarbamol?

Methocarbamol treatment is not time-limited, though healthcare professionals usually prescribe it as a short-term treatment. There are no particular side effects associated with long-term use. 

Methocarbamol contraindications

Methocarbamol cannot be given to anyone with known allergies to the medicine or its inactive ingredients. 

Pregnancy and breastfeeding

The FDA advises that methocarbamol be used in pregnancy only when necessary. People who are breastfeeding should also consider alternative treatments.

Children

Methocarbamol is used in children only to treat tetanus. 

Seniors

Because of the risk of side effects, methocarbamol and other muscle relaxants should only be used with great caution in older adults. 

Methocarbamol warnings

Cautions

Healthcare providers will be more cautious in using methocarbamol by injection to people with certain medical conditions. These include: 

  • Kidney dysfunction: Methocarbamol in IV form or as an intramuscular injection is contraindicated in any person with lowered kidney function. 
  • Seizure disorder: Methocarbamol given in IV form can provoke convulsive seizures in people with a history of seizures. It should also not be used as an intramuscular injection in those with seizure disorders.
  • Latex allergies: Vials of methocarbamol intended for injection have a rubber stopper. This might cause an allergic reaction during an injection. 

Abuse and dependence

Although methocarbamol is a sedative, the FDA does not consider it to have a high risk of abuse. One study concluded that the unpleasant side effects that occur at high doses make it less likely to be misused. In addition, methocarbamol does not have a risk for dependence or withdrawal, as do some other muscle relaxants.

Overdose

Go to an emergency room or call a poison control center if too much methocarbamol is taken. An overdose can be fatal, especially when combined with other CNS depressants such as alcohol. If there’s any uncertainty about an overdose, look for symptoms such as:

  • Nausea
  • Excessive sleepiness
  • Blurred vision
  • Low blood pressure

A severe overdose could cause seizures and coma.

The maximum daily dose of methocarbamol should not exceed eight grams per day when taken for muscle pain or spasms. 

Methocarbamol interactions

While no medications are specifically prohibited, some can cause problems when taken together with methocarbamol. Combining methocarbamol with other CNS depressants will increase the sedative effects of both drugs. This makes people sleepy, less attentive, and more prone to falls and injuries. In the worst cases, people can stop breathing. CNS depressants that can cause problems with methocarbamol include:

How to avoid methocarbamol side effects

Methocarbamol has only a few side effects, but some of these, like sedation and nausea, are commonly experienced. Here are a few tips to minimize these problems.

1. Take methocarbamol as directed

Probably the most important advice is to follow the directions given by the prescriber or written on the prescription label. Methocarbamol may be taken up to several times a day, making it easy to take too many doses by mistake. Use an app or alarm to keep from missing doses, but use a checklist or app to record doses to avoid taking too many.

2. Be careful about missed doses

As with many prescription medications, a missed dose of methocarbamol can be taken when remembered. Unless, of course, it’s almost time for the next dose. Then skip the missed dose and take the next one as scheduled. This prevents taking too much medicine. 

3. Give the prescribing healthcare provider a complete medical history

Another good way to avoid side effects is to make sure the prescriber has a complete medical history. This should include health conditions, medications, dietary supplements, and herbal products. It’s especially important to mention:

  • Kidney disease 
  • Liver disease
  • A history of seizures
  • Any prescriptions for other skeletal muscle relaxants
  • Any use of sedatives, barbiturates, benzodiazepines, or other CNS depressants
  • Any use of Mestinon (pyridostigmine) to treat myasthenia gravis
  • Any alcohol use
  • Pregnancy or any plans to become pregnant
  • Breastfeeding or any plans to breastfeed

4. Take methocarbamol with food

Methocarbamol can be taken on an empty stomach or with a meal or snack. If nausea and indigestion are causing problems, consider taking the methocarbamol tablets with a light snack or meal. 

5. Be careful about driving and other risky activities

The FDA advises caution for the sedative effects of methocarbamol. Potentially risky activities that require attention and responsiveness—like driving, operating machinery, or hazardous sports—should be avoided at first until the effects of the drug are known. After that, engage in these activities cautiously.

6. Remove obstacles from around the house

Driving can be risky when taking sedating drugs. But so can walking around the house. Falls and injuries are serious problems that may occur when taking drugs like methocarbamol. Consider removing obstacles from well-trafficked pathways and make sure that lighting is adequate. 

7. Stop drinking alcohol

Alcohol does not mix well with methocarbamol. The combination can raise the risk of falls, injuries, and side effects. 

8. Avoid medicines and supplements that cause drowsiness

Some prescription drugs that cause sedation may be unavoidable. So be careful when taking them along with methocarbamol. However, there are over-the-counter medications that also put people to sleep and impair mental function. Antihistamines are a good example. Some dietary or herbal supplements also have sedative properties, such as melatonin, kava, and valerian. Take a break from these supplements when taking methocarbamol.

How to treat side effects of methocarbamol

There are some important steps you can take to manage the side effects of methocarbamol.

Drowsiness and dizziness

There’s not much to be done about the drowsiness and dizziness itself, but there are a few things that can keep you from falling and hurting yourself. Stand up slowly. Move slowly and deliberately. Sit down when feeling dizzy and stay seated until it passes. Avoid risky activities like preparing food with a knife, climbing stairs, or driving until the drowsiness or dizziness has passed.

Stomach problems

Talk to the prescribing healthcare provider about treatment options if nausea, vomiting, or upset stomach are a problem.

Allergic reactions

Get immediate medical help at any sign of an allergic reaction including:

  • Hives
  • Trouble breathing
  • Swelling of the face, lips, mouth, or throat
  • Low blood pressure
  • Weak pulse

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