Methocarbamol Stats & Data
GNXFOGHNGIVQEH-UHFFFAOYSA-NPharmacology
DrugBankDescription
Methocarbamol was developed in the early 1950s as a treatment for muscle spasticity and the associated pain. It is a guaiacol glyceryl ether. Methocarbamol tablets and intramuscular injections are prescription medicines indicated in the United States as an adjunct to rest, physical therapy, and other measures for the relief of discomforts associated with acute, painful musculoskeletal conditions. In Canada, methocarbamol can be sold as an over the counter oral medicine at a lower dose that may be combined with acetaminophen or ibuprofen. A combination product with acetylsalicylic acid and codeine is available in Canada by prescription. Methocarbamol was FDA approved on 16 July 1957.
Mechanism of Action
The mechanism of action of methocarbamol is thought to be dependant on its central nervous system depressant activity. This action may be mediated through blocking spinal polysynaptic reflexes, decreasing nerve transmission in spinal and supraspinal polysynaptic pathways, and prolonging the refractory period of muscle cells. Methocarbamol has been found to have no effect on contraction of muscle fibres, motor end plates, or nerve fibres.
Pharmacodynamics
Methacarbamol is a skeletal muscle relaxant with an unknown mechanism of action. Methacarbamol has been shown to block spinal polysynaptic reflexes, decrease nerve transmission in spinal and supraspinal polysynaptic pathways, and prolong the refractory period of muscle cells. Methocarbamol does not act as a local anesthetic upon injection. In animal studies, methocarbamol also prevents convulsions after electric shock.
Metabolism
Methocarbamol is metabolized in the liver by demethylation to 3-(2-hydroxyphenoxy)-1,2-propanediol-1-carbamate or hydroxylation to 3-(4-hydroxy-2-methoxyphenoxy)-1,2-propanediol-1-carbamate. Methocarbamol and its metabolites are conjugated through glucuronidation or sulfation.
Absorption
The time to maximum concentration is 1.1 hours for both healthy patients and those on hemodialysis. The maximum plasma concentration is 21.3mg/L for healthy patients and 28.7mg/L in hemodialysis patients. The area under the curve for healthy patients is 52.5mg/L\*hr and 87.1mg/L*hr in hemodialysis patients. AUC% based on terminal elimination half life is 2% for healthy patients and 4% for hemodialysis patients. Older studies report maximum plasma concentrations in 0.5 hours.
Indication
Methocarbamol tablets and intramuscular injections are indicated in the United States as an adjunct to rest, physical therapy, and other measures for the relief of discomforts associated with acute, painful musculoskeletal conditions. Oral methocarbamol in America may be given up to 1500mg 4 times daily for 2-3 days. In Canada, methocarbamol containing oral formulations are sold over the counter for pain associated with muscle spasm. However, if these combination formulations include codeine, they are prescription only.
Half-life
The elimination half life is 1.14 hours in healthy subjects and 1.24 hours in subjects with renal insufficiency. Older studies report half lives of 1.6-2.15 hours.
Protein Binding
Methocarbamol is 46-50% protein bound in healthy patients and 47.3-48.9% protein bound in hemodialysis patients.
Elimination
In humans the majority of the dose is eliminated in the urine. In dogs, 88.85% of the dose is eliminated in urine and 2.14% in the feces. In rats, 84.5-92.5% of the dose is eliminated in the urine and 0-13.3% is eliminated in the feces.
Volume of Distribution
Volume of distribution data in humans is scarce. In horses, the volume of distribution is 515-942mL/kg at steady state or 724-1130mL/kg.
Measured Affinities
Guide to PHARMACOLOGYMeasured binding and functional data for methocarbamol, curated by the IUPHAR/BPS Guide to PHARMACOLOGY. Each row cites the paper it came from. Lower concentrations mean tighter binding — a value in the sub-nanomolar range indicates a very potent interaction.
| Target | Action | Measure | Value | Concentration | Species | Source |
|---|---|---|---|---|---|---|
| carbonic anhydrase 1 CA1 | Inhibition | pKi | 7.6 | 25.12 nM | Human | PMID 17125255 |
Reading this. pKi, pEC50 and pIC50 are negative log molar values, so a higher number means a tighter interaction; the concentration column converts them for you. Values from non-human species are laboratory measurements and do not translate directly to human effect. Receptor affinity is not a dose — it describes what a molecule binds, not how much of it is safe to take.
Receptor data from the IUPHAR/BPS Guide to PHARMACOLOGY (v2026.2), licensed CC BY-SA 4.0. Matched to this substance by InChIKey.
Signs and Symptoms of Overdose Isolated methocarbamol overdose is rare and unlikely to be life-threatening in the absence of multiple drug exposures. Based on limited data, toxicity symptoms may include nausea, sedation, seizures, coma, and death. Management of Overdose
Liver injury risk
Ambiguous (limited data)
Toxicity (DrugBank)
Overdose of methocarbamol may be associated with alcohol and other central nervous system depressants. Patients may experience nausea, drowsiness, blurred vision, hypotension, seizures, and coma. Treatment of overdose is generally through airway maintenance, monitoring urinary output, vital signs, and giving fluid intravenously if necessary. The oral LD50 in rats is 3576.2mg/kg. The FDA has classified methocarbamol as pregnancy category C. Animal and human studies have not been performed to determine the risks to a fetus, however fetal and congenital abnormalities have been reported. Methocarbamol is excreted in the milk of dogs, however it is unknown if this is also the case for humans. Caution should be exercised when taking methocarbamol while breastfeeding. Studies to assess the carcinogenicity, mutagenicity, or effects on fertility of methocarbamol have not been performed.
Tolerance & Pharmacokinetics
drugs.wikiTolerance Decay
Experience Report Analysis
ErowidDemographics
Gender Distribution
Too few reports for a chart: gender is known from 15 reports, and a split is drawn only from 20 reports or more. Counts are shown instead. Why 20?
- Male 14 of 15
- Not Specified 1 of 15
Age Distribution
Reports Over Time
Effect Analysis
ErowidEffects aggregated from 9 experience reports (9 single-substance Erowid)
Effect Sentiment Distribution
Confidence Distribution
Each bar is the share of reports mentioning the effect; its whisker, and the band on the rows below, is the 95% interval: where the share could plausibly be with other reports of the same kind.
Too few reports for bars: these effects come from 9 single-substance Erowid reports, and a bar is drawn only from 20 reports or more. With fewer, a percentage cannot tell a common effect from a rare one. Counts are shown instead. Why 20?
Positive Effects 0
Adverse Effects 1
Also reported in combinations. In the 6 Methocarbamol reports where another drug was taken too, 1 mentions hospital, emergency services or an overdose, 0 a seizure and 0 psychosis (too few reports for percentages). In the 9 single-substance reports: 1, 0 and 0. These are not in the figures above: they cannot be put down to Methocarbamol alone, and a mention is not always something that happened to the writer.
Dosage Distribution
Dose distribution from experience reports, one dose per report (the first listed). Doses above Q3 + 3×IQR, far above what people typically take, are left out of the median and range and listed under each route: most are real heavy doses or overdoses, not mistakes.
Real-World Dose Distribution
ErowidFrom 19 of 19 recorded dose entries: those that state a weight (mg, g or µg), in routes with at least five of them. Values above Q3 + 3×IQR, far above what people typically take, are left out; they can include real heavy doses and overdoses, not only mistakes.
Oral (n=18)
Form / Preparation
Most common forms and preparations, as a share of the 10 reports that give one
Too few reports for bars: these forms come from 10 reports, and a bar is drawn only from 20 reports or more. With fewer, a percentage cannot tell a common effect from a rare one. Counts are shown instead. Why 20?
- Pill / Tablet 10 of 10
Body-Weight Dosing
Dose per kg of body weight, one dose per report (the first listed), from reports giving a weight of 30–250 kg. Doses above Q3 + 3×IQR, far above what people typically take, are left out of the median and range and listed under each route.
1 report gave a dose above the typical range (224.839 mg/kg), so it is not in the figures above. Listing a dose here does not mean it is safe.
Show the report
Redose Patterns
Redosing behavior across 12 reports
Too few reports for a chart: redosing is known from 12 reports, and a split is drawn only from 20 reports or more. Counts are shown instead. Why 20?
- Single dose 7 of 12
- Redosed 5 of 12