Methocarbamol Drug Interactions: What to Avoid and What to Tell Your Doctor

Methocarbamol is a CNS depressant — and that single fact drives most of its significant drug interactions. When you combine CNS depressants, the effects multiply, not just add. Here's a thorough guide to what you need to know about Methocarbamol interactions before you start taking it.

The Most Dangerous Interactions: CNS Depressants

Methocarbamol's product label includes a specific warning about combining it with other CNS depressants. The combinations below can cause profound sedation, respiratory depression (slowed breathing), coma, and death.

Alcohol

Alcohol + Methocarbamol is one of the most important interactions to avoid. Both are CNS depressants, and the combination amplifies sedation to a dangerous degree. Overdose deaths have been reported with Methocarbamol alone, and the risk increases dramatically when combined with alcohol or other CNS depressants. Do not drink alcohol at all while taking Methocarbamol.

Opioids (Prescription Pain Medications)

Combining Methocarbamol with opioid pain medications (such as oxycodone, hydrocodone, codeine, tramadol, morphine) can cause profound sedation, respiratory depression, coma, and death. This is a major drug-drug interaction. Patients who are prescribed both a muscle relaxant and an opioid should be closely monitored by their provider — and the combination should only be used when the clinical benefit clearly outweighs the risk.

Benzodiazepines

Benzodiazepines such as diazepam (Valium), alprazolam (Xanax), lorazepam (Ativan), and clonazepam (Klonopin) are CNS depressants. Combining them with Methocarbamol potentiates the CNS-depressant effects of both drugs and significantly increases sedation, respiratory depression, and fall risk. Monitor closely if both are prescribed simultaneously.

Sleep Medications

Sleep aids — both prescription (zolpidem/Ambien, eszopiclone/Lunesta, zaleplon/Sonata) and OTC (diphenhydramine/Benadryl, doxylamine/Unisom) — are CNS depressants. Combining them with Methocarbamol can increase the risk of excessive sedation. Avoid taking sleep aids while on Methocarbamol unless directed by your doctor.

Other Muscle Relaxants

Taking multiple muscle relaxants together (e.g., Methocarbamol + cyclobenzaprine or Methocarbamol + carisoprodol) adds CNS depression on top of CNS depression. This combination is rarely clinically appropriate and significantly increases the risk of oversedation, respiratory depression, and falls.

Anti-Anxiety Medications

Anxiety medications that cause CNS depression (including buspirone, hydroxyzine, and others) can interact with Methocarbamol. The combination increases sedation risk. Tell your doctor about any anxiety medication you're taking.

Specific Drug-Specific Interactions

Pyridostigmine (for Myasthenia Gravis)

Methocarbamol may reduce the effectiveness of pyridostigmine bromide, a medication used to treat myasthenia gravis (a neuromuscular disorder). Patients with myasthenia gravis who take pyridostigmine should use Methocarbamol with caution and only under close medical supervision.

Interactions With Laboratory Tests (Not a Drug, But Important)

Methocarbamol can cause false-positive results in certain urine screening tests:

5-HIAA test: Can cause false-positives when testing for 5-hydroxyindoleacetic acid (used to screen for carcinoid tumors) using the nitrosonaphthol reagent method

VMA test: Can cause false-positive results in urinary vanillylmandelic acid testing (used to screen for certain adrenal tumors) using the Gitlow method

Always inform your healthcare provider and laboratory technician that you are taking Methocarbamol before these tests are performed.

What About NSAIDs?

There is no known significant drug interaction between Methocarbamol and non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen (Advil, Motrin), naproxen (Aleve), or diclofenac. In fact, NSAIDs are sometimes prescribed alongside Methocarbamol for acute musculoskeletal pain — the NSAID targets inflammation while Methocarbamol addresses the spasm. A methocarbamol/ibuprofen combination product is even sold under the brand name Summit Ultra.

Full List of Things to Tell Your Doctor

Before starting Methocarbamol, tell your doctor if you take any of the following:

Any opioid pain medications (oxycodone, hydrocodone, morphine, codeine, tramadol)

Benzodiazepines (Xanax, Valium, Ativan, Klonopin, etc.)

Sleep medications — prescription or OTC

Antihistamines that cause drowsiness (Benadryl, Unisom)

Antidepressants and anti-anxiety medications

Antipsychotic medications

Any other muscle relaxants

Pyridostigmine (for myasthenia gravis)

All herbal supplements and OTC products — many have sedative effects

For a full discussion of side effects alongside these interactions, see: Methocarbamol Side Effects: What to Expect and When to Call Your Doctor.

If you're having trouble finding Methocarbamol at a pharmacy near you, medfinder can check availability for you.