Carisoprodol

Isopropyl meprobamate

Soma, Vanadom, Rela, Carisoma, Somadril

Psychoactive Class

Depressant Sedative Muscle Relaxant Anxiolytic GABAergic

Chemical Class

Carisoprodol is a carbamate sedative-hypnotic and centrally acting muscle relaxant first approved for medical use in 1959.¹² Developed as an improvement upon meprobamate, it functions as a prodrug that is metabolized into meprobamate in the body.³² Prescribed for the short-term treatment of musculoskeletal pain, it also possesses anxiolytic and hypnotic properties.¹ Its effects are often compared to barbiturates, and it has been largely supplanted by benzodiazepines due to safety concerns. Its European Union approval was withdrawn in 2008.⁴

Dosage & Duration

Dosage

Threshold50-50 mg

Light100-350 mg

Moderate350-700 mg

Strong700+ mg

Heavy750+ mg

Duration

Onset15-60 minutes

Peak2-5 hours

After Effects1-12 hours

Half-life

~2 hours

Subjective Effects

The experience is dominated by sedation, muscle relaxation, and anxiety relief, with an overall character frequently compared to barbiturates, benzodiazepines, and alcohol. At common doses the effects are often unremarkable — a heady, dreamy lethargy with relaxation but little mood lift — while stronger doses more reliably produce cognitive and physical euphoria, and very high doses are associated with a hypomanic-like state of cheerfulness, disinhibition, sociability, and psychomotor excitement alongside marked impairment. Any euphoria tends to be short-lived owing to the drug's rapid metabolism into meprobamate, and is thought to stem largely from carisoprodol's potent anxiolytic action. Responses vary considerably: even at high doses, some users primarily encounter sedation, depression, and dysphoria rather than positive effects.

Physical

The body feel centers on heavy sedation and pronounced muscle relaxation, accompanied by lethargy, dizziness, and impaired coordination. Physical euphoria at stronger doses is often described as more prominent than that of benzodiazepines.

Impairment

Dizziness

Sedation

Uncomfortable

Headache

Cognitive

The headspace is relaxed, anxiolytic, and somewhat zoned-out, with disinhibition and increased sociability emerging at stronger doses. Memory of the experience can be impaired, and total amnesia of the period after ingestion is not uncommon following heavy use or overdose.

Emotional

Suppressions

Visual

Visual effects are largely absent at typical doses; blurred vision and nystagmus are associated with overdose.

Reagent Testing

Loading reagent data

Expected colorimetric results are being prepared.

Pharmacology

Pharmacodynamics

Carisoprodol is a centrally acting muscle relaxant that functions through both positive allosteric modulation and direct agonism at GABA-A receptors, with evidence suggesting separate binding sites for each mechanism, both of which appear distinct from those used by benzodiazepines and barbiturates.⁵⁶ Its muscle relaxant effects are associated with altered interneuronal activity in the spinal cord and descending reticular formation.¹ The drug shows subunit-dependent selectivity, with direct agonist activity more pronounced at α2-containing receptors and positive allosteric modulation showing greater efficacy at α1 and β2-containing complexes.⁶ In animal studies, flumazenil has been shown to partially inhibit the drug's activity.⁵

Pharmacokinetics

Carisoprodol is metabolized in the liver primarily by CYP2C19, with a considerable proportion converted to meprobamate, an active metabolite that functions as a GABA-A receptor modulator and adenosine reuptake inhibitor.¹ Meprobamate reaches higher peak plasma concentrations than carisoprodol itself and has a substantially longer half-life of approximately 11.3 hours. Additional metabolites include hydroxycarisoprodol and hydroxymeprobamate. The reported elimination half-life of carisoprodol is approximately 2 hours according to some sources and approximately 8 hours according to others.¹ Excretion occurs via the kidneys.¹

Interactions

Dangerous

Highest risk

These combinations are considered extremely harmful and should always be avoided. Reactions to these drugs taken in combination are highly unpredictable and have a potential to cause death.

DissociativesStimulants

Caution

Use caution

These combinations are not usually physically harmful, but may produce undesirable effects, such as physical discomfort or overstimulation. Extreme use may cause physical health issues. Synergistic effects may be unpredictable. Care should be taken when choosing to use this combination.

1,2-BenzodiazepineAbataceptAbrocitinibAcenocoumarolAcetazolamide

TripSit

Tolerance

Full Tolerance

Tolerance develops to the sedative-hypnotic effects following prolonged use. The accumulation of the active metabolite meprobamate, which has a longer half-life, contributes to the development of tolerance and complicates the tolerance profile with chronic administration.

Cross Tolerance

Other carbamates (meprobamate), Barbiturates, GABAergic sedative-hypnotics

Baseline Reset

The exact timeframe for tolerance to return to baseline is not well established. Due to the accumulation of meprobamate with chronic use, complete tolerance reset may require an extended period of abstinence.

Harm Potential

Addiction & Dependence

Psychological

High

Carisoprodol has significant psychological addiction potential with documented abuse cases even when used without other drugs possessing abuse potential.⁷ Compulsive redosing is a recognized effect, and users frequently escalate to very high daily doses.⁸ Its potent anxiolytic effects and euphoria are implicated in drug-seeking behavior.² Psychological dependence is more common in those who use it non-medically or have a history of substance use.⁷

Physical

Extremely High

Physical dependence of the barbiturate type develops following prolonged use.² Withdrawal can be life-threatening, particularly in high-dose users or those who stop abruptly, and may require hospitalization.⁹ Severe withdrawal can mimic alcohol withdrawal including potentially lethal status epilepticus.⁷⁹ The accumulation of meprobamate, which has a longer half-life, contributes to withdrawal severity.⁸

Toxicity

Central Nervous System

Overdose causes CNS depression ranging from lethargy to deep coma; chronic use and withdrawal can result in prolonged cognitive changes including memory impairment, reduced IQ, increased anxiety and depression, and in some cases these effects persist for months or years after discontinuation.²

Respiratory

Respiratory depression occurs primarily in overdose situations and is significantly more dangerous when carisoprodol is combined with other CNS depressants; mechanical ventilation may be required in severe cases.⁷

Psychosis Risk

Psychotic symptoms occur primarily during withdrawal rather than acute intoxication.⁸ Approximately 20% of withdrawal cases feature hallucinations (mainly visual and auditory) or other psychotic symptoms. Case reports document patients experiencing vivid hallucinations of insects, animals, people, and voices indistinguishable from reality, along with paranoid ideation.¹¹ Symptoms typically peak 3-5 days after cessation and may last up to 8-9 days.⁸

Seizure Risk

Unlike benzodiazepines, carisoprodol increases rather than decreases seizure risk.⁹ Seizures can occur both in overdose and during withdrawal.⁷² Withdrawal seizures can progress to potentially lethal status epilepticus, similar to alcohol withdrawal.⁹ Drugs that lower seizure threshold should be avoided during withdrawal. Deaths have been reported in association with carisoprodol-related seizures.⁷

History & Culture

Discovery and Development

Frank M. Berger at Wallace Laboratories (later Carter-Wallace) synthesized carisoprodol in 1956.¹² Berger had also been part of the team responsible for creating meprobamate, which had become a widely used pharmaceutical during the…

Legality

International

1961 Single Convention: carisoprodol is not scheduled.

1971 Convention on Psychotropic Substances: Schedule IV.

1988 Convention: carisoprodol is not listed in precursor Tables I or II.

By Country

United StatesPrescription onlySchedule IV controlled substance

21 CFR § 1308.14(c)²⁵

Current official national law establishes the stated carisoprodol control in United States; lawful medical handling remains subject to the cited regime.

CanadaRestrictedFederally controlled substance

Controlled Drugs and Substances Act and regulations²²

Current official national law establishes the stated carisoprodol control in Canada; lawful medical handling remains subject to the cited regime.

FinlandNo longer availableCitation needed

Carisoprodol is no longer available in Finland, including as a prescription medication.¹⁹ Previously marketed as Somadril.

IndonesiaWithdrawn from marketCitation needed

Taken off the market in September 2013 due to concerns about diversion, dependence, and adverse effects.²⁰

NorwayWithdrawn from marketCitation needed

Removed from the market in May 2008 following reports demonstrating addictive potential as a prodrug of meprobamate and as a potentiator of opioid medications including hydrocodone, oxycodone, and codeine.²⁴¹⁹

SwedenWithdrawn from marketCitation needed

Taken off the market in November 2007 due to problems with dependence and side effects.¹⁹ The Swedish pharmaceutical regulatory agency determined that alternative medications offered comparable or better efficacy without the associated risks.

AustraliaNo longer registeredCitation needed

Removed from the Australian Register of Therapeutic Goods. Access is still possible through the Special Access Scheme for individual patient needs.²⁰

European UnionMarketing authorization withdrawnCitation needed

The European Medicines Agency recommended member states suspend marketing authorization in 2008 due to concerns about dependence and insufficient benefit-risk profile for acute back pain treatment.¹⁹

GermanyPrescription onlyAnlage III controlled prescription

Betäubungsmittelgesetz, Anlage III²³

Carisoprodol is listed in Anlage III of the BtMG as a marketable and prescribable controlled substance.

MexicoAvailable without prescriptionCitation needed

Sold over-the-counter, though typically in lower doses than those available in the United States. Commonly advertised in border cities.

SpainOver-the-counter (unconfirmed)Citation needed

Reports indicate carisoprodol may be available without prescription, though this has not been officially confirmed.

ThailandOver-the-counter (unconfirmed)Citation needed

As of 2005, reported to be available without prescription in combination formulations with phenylbutazone or paracetamol. Status may have changed since then.

References

Source Pages

Citations

Automated synthesis
Information aggregated and synthesized using an autonomous workflow built by Josie Kins.

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