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Systematic (IUPAC) name
2-hydroxy-3-(2-methoxyphenoxy)propyl carbamate
Clinical data
  • C
Routes of
Oral, intravenous
Legal status
Legal status
Pharmacokinetic data
Metabolism Hepatic
Biological half-life 1.14-1.24 hours[1]
CAS Number 532-03-6
ATC code M03BA03 (WHO)
PubChem CID 4107
DrugBank APRD01102
Chemical data
Formula C11H15NO5
Molar mass 241.241 g/mol[[Script error: No such module "String".]]
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Methocarbamol (trade name Robaxin) is a central muscle relaxant used to treat skeletal muscle spasms. It is the carbamate of guaifenesin, but does not produce guaifenesin as a metabolite, since the carbamate bond is not hydrolyzed metabolically; metabolism is by Phase I ring hydroxylation and O-demethylation, followed by Phase II conjugation. All of the major metabolites are unhydrolyzed carbamates.[2][3]

Methocarbamol is marketed under different names when presented in combination with other active ingredients. In combination with acetaminophen (Paracetamol), its trade name is Robaxacet, whereas Robax Platinum is the trade name for a formulation of methocarbamol and ibuprofen.[4] A combination of methocarbamol and aspirin is marketed as Robaxisal. Unlike other carbamates such as carisoprodol and meprobamate, Methocarbamol has little to no abuse potential, although it is not uncommon to see abuse.

Methocarbamol with acetaminophen, and methocarbamol with ibuprofen are both sold as Nuprin Muscle & Back Pain Relief for the Shoppers Drug Mart chain in Canada.

Potential side effects include: drowsiness, dizziness, upset stomach, flushing, blurred vision, and fever. Contact a doctor if these symptoms persist. Serious side-effects include the development of a severe skin rash or itching, slow heart rate, fainting, jaundice, persistent nausea/vomiting, stomach/abdominal pain, mental/mood changes, clumsiness, trouble urinating, signs of infection. [5] Contact a doctor immediately if these symptoms are experienced. Additionally, methocarbamol may cause urine to turn black, blue, or green. However, this effect is harmless.[6]

Because of potential for side effects, this drug is on the list for High Risk Medications in the elderly. (See NCQA’s HEDIS Measure: Use of High Risk Medications in the Elderly,


  1. Sica DA, Comstock TJ, Davis J, Manning L, Powell R, Melikian A, Wright G. (1990). "Pharmacokinetics and protein binding of methocarbamol in renal insufficiency and normals". European Journal of Clinical Pharmacology. 39 (2): 193–4. doi:10.1007/BF00280060. PMID 2253675. 
  2. Methocarbamol. In: DRUGDEX System [intranet database]. Greenwood Village, Colorado: Thomson Healthcare; c1974–2009 [cited 2009 Feb 10].
  3. Bruce RB, Turnbull LB, Newman JH. (1971 Jan). "Metabolism of methocarbamol in the rat, dog, and human". J Pharm Sci. 60 (1): 104–106. doi:10.1002/jps.2600600120. PMID 5548215.  Check date values in: |date= (help)
  4. "New Drugs and Indications Reviewed at the May 2003 DEC Meeting" (PDF). ESI Canada. Retrieved 2008-11-14.