Benadryl With Robaxin Interaction

There is a moderate drug interaction Benadryl (diphenhydramine) and Robaxin (methocarbamol). They should be used cautiously together.


I was recently prescribed Robaxin (methocarbamol). I take Benadryl every once in a while to sleep. Are Benadryl and Robaxin safe to take together?

Asked by Jerry On Nov 09, 2018

Answered by
Medical Content Reviewed By PharmacistAnswers Staff

On Nov 09, 2018
Drug Interaction


There is a moderate interaction between Benadryl (diphenhydramine) and Robaxin (methocarbamol). Not only are both sedating, they are both CNS (central nervous system) depressants and can have additive effects if taken together.

Use caution if taking both together.


Benadryl (diphenhydramine) is a sedating antihistamine, also known as a H1-blocker. It is available in a variety of dosage forms, including oral, topical, and parenteral products. 

It is a "first-generation" antihistamine of the ethanolamine class, which are associated with significant sedation in most individuals. It also has strong anticholinergic properties, which can cause dizziness, dry mouth, dry eyes and constipation.

After taking a dose by mouth, the onset of action of Benadryl is around 15-30 minutes and peak effects occur in 1 to 3 hours. The typical duration of action is around 4 to 6 hours, although this is generally extended in certain populations, such as in the elderly and in those with liver disease.

Central nervous depression with Benadryl is manifested as:

  • Drowsiness
  • Dizziness
  • Muscle weakness
  • Confusion
  • Slurred speech
  • Fatigue
  • Physical weakness
  • Headache

Caution is recommended when combining Benadryl with other CNS depressants. Side effects can be additive. 

More information regarding Benadryl can be found here:


Robaxin (methocarbamol) is a central nervous system depressant, with sedative and muscle relaxant properties.

Robaxin is rapidly absorbed from the gastrointestinal tract and has an onset of action within 30 minutes after oral administration. Peak concentrations occur approximately 1 to 2 hours after taking a dose.

Robaxin can be taken with or without food.

As with other CNS depressants, Robaxin can cause the following adverse effects:

  • Dizziness
  • Sedation
  • Confusion
  • Headaches

    Robaxin needs to be used cautiously with other drugs possessing CNS depressant effects.

    Additional information regarding Robaxin can be found here:


    As discussed above, both Robaxin and Benadryl have central nervous system depressant effects. Taking them together may cause additive CNS depression (e.g. sedation, dizziness). If you have been directed to take both by your doctor, you may need to adjust the dose of either or both medications

    It is important to remember that both Benadryl and Robaxin can impair your ability to drive and complete tasks requiring mental alertness.

    You can read more about this interaction and others here:

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