Thiopental

5-ethyl-5-pentan-2-yl-2-sulfanylidene-1,3-diazinane-4,6-dione

Overview

Thiopental belongs to Depressants.

Key safety note: Thiopental produces profound respiratory and cardiovascular depression with no ceiling effect and a low therapeutic index, so it is given only by anaesthetists able to manage a lost airway and support the circulation.[2]
Effects
Subjective effects vary. What a substance feels like depends on dose, individual physiology, mindset, and setting. The points below describe commonly reported effects, not guaranteed, uniform, or desirable outcomes.
  • Given IV: near-instant drowsiness with a metallic/garlic taste, then loss of consciousness within seconds.
  • Deep anaesthesia with slowed or absent breathing and lowered blood pressure.
  • Rapid awakening after a single dose (minutes) as it redistributes, often with residual grogginess. Prolonged sedation after repeated dosing.
Dosing & duration
Harm-reduction note: These are commonly cited reference ranges, not a recommendation or a “safe” dose. Potency, purity, body chemistry, tolerance, and drug combinations vary widely. Start low, go slow, wait for full effects before redosing, and never assume an unknown product matches these figures. Missing data is not evidence of safety.

Intravenous only, administered by an anaesthetist. Figures below are clinical context, NOT a recreational guide.. Thiopental is titrated intravenously to loss of consciousness by clinicians equipped to manage apnoea and hypotension. There is no safe non-medical use. Its brief action after a single dose is due to redistribution, so repeated boluses or infusions accumulate and prolong recovery unpredictably.

Dose ranges

Anaesthetic induction (adult, IV)

≈3–5 mg/kg, titrated

Barbiturate coma (ICU)

IV loading + infusion, specialist-titrated to EEG

Duration

onset

IV ≈30–45 s

total

Single dose ≈5–10 min (redistribution)

after effects

Residual sedation. Markedly prolonged after repeated/continuous dosing

Chemical & Physical Properties
FormulaC11H18N2O2S
Molar mass242.34 g/mol
StateSolid
Melting pointNot reported
Boiling pointNot reported
DensityNot reported
Vapor pressureNot reported
pKa7.55
LogP2.85
Solubility3.98×10⁻² g/L
Refractive indexNot reported
Identifiers & Synonyms
CAS76-75-5
CAS (enantiomer)
PubChem CID3000715
InChIKeyIUJDSEJGGMCXSG-UHFFFAOYSA-N
InChIInChI=1S/C11H18N2O2S/c1-4-6-7(3)11(5-2)8(14)12-10(16)13-9(11)15/h7H,4-6H2,1-3H3,(H2,12,13,14,15,16)
SMILESCCCC(C)C1(C(=O)NC(=S)NC1=O)CC

Synonyms

  • Sodium thiopental
  • Thiopentone
  • Pentothal
  • Trapanal
Pharmacodynamics & Biochemistry

Thiopental (Pentothal, sodium thiopental) is an ultra-short-acting thiobarbiturate: the sulphur analogue of pentobarbital. Like other barbiturates it is a positive allosteric modulator of the GABA-A receptor, prolonging GABA-evoked chloride-channel opening and, at anaesthetic concentrations, opening the channel directly. It also blocks neuronal nicotinic acetylcholine receptors. The result is rapid, dose-dependent CNS depression with no ceiling: deep enough for surgical anaesthesia and, in overdose, for fatal respiratory and cardiovascular collapse. Its hallmark is its kinetics. Given intravenously it is so lipophilic that it reaches the brain and produces unconsciousness within about 30–45 seconds, but consciousness returns after only ≈5–10 minutes, not because the drug is eliminated, but because it redistributes out of the brain into muscle and fat. Its actual terminal elimination half-life is long (≈5.5–26 h) and it is metabolised in the liver (partly to pentobarbital), so repeated or continuous dosing accumulates and greatly prolongs recovery (a 'context-sensitive' effect). This rapid on/off single-dose profile made thiopental a classic intravenous induction agent. The same reliable, deep suppression underlies its use in barbiturate coma, its historical reputation as a 'truth serum', and its role as the first drug in lethal-injection protocols.

Biological targets

  • GABA-A
Pharmacokinetics
BioavailabilityIV (100%)
TmaxNot reported
Half-lifeClinical ≈5–10 min (redistribution), terminal ≈5.5–26 h
VdNot reported
Protein bindingNot reported
MetabolismHepatic (major metabolite pentobarbital)
ExcretionRenal (metabolites)
Toxicology & Safety
Harm-reduction note: Toxicity and risk depend on dose, route, purity, combinations, setting, and individual health factors. Missing harms should never be interpreted as evidence of safety.

Not reported

Thiopental produces profound respiratory and cardiovascular depression with no ceiling effect and a low therapeutic index, so it is given only by anaesthetists able to manage a lost airway and support the circulation. Even an induction dose causes apnoea and a fall in blood pressure. It is dangerous with any other CNS depressant. There is no specific antidote (flumazenil does not reverse barbiturates). Management is supportive. Extravasation or accidental intra-arterial injection can cause severe tissue damage. Repeated dosing accumulates, its clinical brevity is redistribution, not elimination, prolonging sedation. It is not a drug of casual misuse, but its reliable lethality is why it has been used for capital punishment and euthanasia.[2]

Legal Status
Legal note: Legal status can change over time and may vary by country, region, formulation, analogue status, prescription context, and enforcement practice. Always confirm with current official sources before relying on this section.
Interactions & Contraindications

Drug interactions

Alcohol, Opioids, Benzodiazepines, General anaesthetics and other sedatives Additive, potentially fatal respiratory and cardiovascular depression, including with volatile anaesthetics.[2]

Contraindications

Acute intermittent or related porphyria barbiturates can precipitate an acute attack.[2]
Cardiovascular disease, hypertension or arrhythmia severe hypovolaemia, shock or unstable cardiovascular disease (risk of profound hypotension).[2]
Significant respiratory depression or acute severe asthma status asthmaticus.[2]
Known hypersensitivity to the drug barbiturate hypersensitivity.[2]
Usage & Context
  • An intravenous anaesthetic used to induce general anaesthesia (rapid 'off' after a single dose) and, by infusion, to produce a barbiturate coma for refractory status epilepticus and dangerously raised intracranial pressure.
  • Historically promoted as a 'truth serum' for interrogation (its reliability for that is disputed), and used as the first agent in three-drug lethal-injection protocols and in euthanasia.
  • Its manufacture has largely ceased in the West: the sole US maker (Hospira) stopped production in 2011 and the EU banned its export for use in executions, so it has become scarce.
Sources & Evidence

Further Information