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Clomethiazole

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Subjective Effects
Interactions
Legality
Clomethiazole molecule structureClomethiazole molecule structure
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Clomethiazole, classified as a sedative and hypnotic1, is a depressant with barbiturate-like effects. Clomethiazole as Heminevrin 0.8% infusion has been used to treat acute alcohol-withdrawal symptoms in hospital when oral administration is not practicable2. Its sedative, anti-anxiety (qualified as “some anti-anxiety effects”)1, and anticonvulsant1 actions distinguish it from its vitamin-derived structure. The drug has relatively high toxicity compared with benzodiazepines and may be especially hazardous for people with personal or familial addiction histories.

Dosage & Duration

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Dosage

Doses are population estimates that vary widely between individuals.

Threshold100 mg
Light100-150 mg
Moderate150-200 mg
Heavy200+ mg

Duration

Onset15-40 minutes
After Effects1-16 hours
Total5-8 hours

Subjective Effects

Subjective Effects not written up yet

Pharmacology

Pharmacodynamics

In vitro, preincubation with clomethiazole dose-dependently potentiated muscimol's inhibition of prolactin release from rat hemiadenohypophysis; picrotoxin antagonized this effect.3 It also increased chloride uptake into rat cortical synaptoneurosomes in a concentration-dependent, picrotoxin-sensitive manner.4 Unlike barbiturates, it does not affect electrophysiological responses to excitatory amino acids.

Pharmacokinetics

Clomethiazole efficiently inhibits chlorzoxazone metabolism and thus CYP2E1 activity in humans5 and also inhibits CYP2B6, with possible inhibition of CYP2A6, which can slow the metabolism or plasma clearance of their substrates, including ethanol. The article cites a prior study reporting a 30% increase in clomethiazole clearance after carbamazepine treatment and reports a 40% increase in patients taking enzyme-inducing drugs.6

Metabolitesnone documented yet

Interactions

Interactions not written up yet

An unlisted combination is an unknown one, not a safe one. Check a dedicated combination chart before mixing.

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Tolerance

Tolerance timelines are rules of thumb, not exact schedules, and vary widely between individuals and use patterns.

Full Tolerance
Long-term and frequent use can cause tolerance.

Harm Potential

Addiction & Dependence

Psychological

High

Classified as habit-forming with significant abuse potential. Not recommended for patients with personal or familial history of addiction due to elevated risk for drug abuse.

Physical

High

Frequent long-term use may lead to tolerance and physical dependence. Stopping abruptly can produce withdrawal effects resembling those seen after sudden cessation of alcohol, short-acting barbiturates, or short-acting benzodiazepines.

Toxicity

Lethal Dosage

Particularly toxic and dangerous in overdose, potentially fatal. Alcohol multiplies the effect. The benzodiazepine antidote flumazenil cannot reverse overdose effects due to clomethiazole's unique chemical structure; treatment is restricted to mechanical ventilation until the drug is metabolized or excreted. Keith Moon of The Who died of a clomethiazole overdose.

History & Culture

Clomethiazole, also called chlormethiazole, was developed by Hoffmann-La Roche in the 1930s. It is used to treat alcohol withdrawal symptoms under close hospital supervision7 and marketed under names including Heminevrin in the United…

Legality

Legality not written up yet

References

Citations

  1. WHO Expert Committee on Drug Dependence: Twenty-fourth Report. World Health Organization (1988). https://ecddrepository.org/sites/default/files/2023-04/who_trs_761_text_version.pdf123
  2. Heminevrin 0.8% Infusion Summary of Product Characteristics. Irish Medicines Board (2006). https://assets.hpra.ie/products/Human/23502/LicenseSPC_PA0970-040-001_11112006020733.pdf1
  3. Evidence that clomethiazole interacts with the macromolecular GABA A-receptor complex in the central nervous system and in the anterior pituitary gland. PubMed (1989). https://pubmed.ncbi.nlm.nih.gov/254481112
  4. Chlormethiazole: neurochemical actions at the gamma-aminobutyric acid receptor complex. PubMed (1989). https://pubmed.ncbi.nlm.nih.gov/25467851
  5. Chlormethiazole inhibition of cytochrome P450 2E1 as assessed by chlorzoxazone hydroxylation in humans. PubMed (1997). https://doi.org/10.1002/hep.5102604231
  6. Population pharmacokinetics of clomethiazole and its effect on the natural course of sedation in acute stroke patients. British Journal of Clinical Pharmacology (2007). https://pmc.ncbi.nlm.nih.gov/articles/PMC18842881
  7. Heminevrin 31.5 mg/ml Syrup - Summary of Product Characteristics. electronic Medicines Compendium (emc) (2025). https://www.medicines.org.uk/emc/product/2496/smpc12
  8. Postmortem toxicology findings from medicolegal investigations of drug-related deaths among the rich and famous. ResearchGate; Toxicologie Analytique et Clinique (2017). https://doi.org/10.1016/j.toxac.2017.04.0011

Article Status

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