Secobarbital

5-pentan-2-yl-5-prop-2-enyl-1,3-diazinane-2,4,6-trione

Overview

Secobarbital belongs to Depressants.

Key safety note: Secobarbital shares the barbiturate hazards: a low therapeutic index and no ceiling on respiratory depression, so a hypnotic dose and a fatal dose are dangerously close, and closer still with tolerance or when combined with alcohol, opioids or benzodiazepines.[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.
  • Rapid sedation, drowsiness and sleep. At sub-hypnotic doses a disinhibited, 'drunk' euphoria that drove its recreational use as 'reds'.
  • Slurred speech, unsteadiness, and impaired coordination, memory and judgement.
  • With regular use: rapid tolerance, strong physical dependence, and a dangerous withdrawal on stopping.
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.

Oral (historically capsules): clinician-prescribed. Figures below are historical clinical context, NOT a recreational guide. Secobarbital is also used at high doses in assisted dying, underlining its narrow safety margin.. Secobarbital's hypnotic dose sits close to its dangerous and lethal range, with no ceiling on respiratory depression and no antidote, and the margin shrinks with tolerance and with any other depressant. It must never be stopped abruptly after regular use.

Dose ranges

Hypnotic (historical, oral)

≈100 mg at bedtime (adult)

Preoperative sedation (historical)

≈200–300 mg

Duration

onset

≈15–30 min

total

Hypnotic effect ≈3–4 h (elimination half-life ≈15–40 h)

after effects

Residual sedation. Withdrawal on cessation after regular use

Chemical & Physical Properties
FormulaC12H18N2O3
Molar mass238.28 g/mol
StateSolid
Melting point100 °C
Boiling pointNot reported
DensityNot reported
Vapor pressureNot reported
pKa7.8
LogP1.97
Solubility550 mg/L, Very slightly soluble in water. Freely soluble in alcohol and ether, and in solutions of fixed alkali hydroxides and carbonates. Soluble in chloroform, Very lipid sol
Refractive index1.4936 at 25 °C (D line), crystal indices nα 1.487, nβ 1.557, nγ 1.563
Identifiers & Synonyms
CAS76-73-3
CAS (enantiomer)
PubChem CID5193
InChIKeyKQPKPCNLIDLUMF-UHFFFAOYSA-N
InChIInChI=1S/C12H18N2O3/c1-4-6-8(3)12(7-5-2)9(15)13-11(17)14-10(12)16/h5,8H,2,4,6-7H2,1,3H3,(H2,13,14,15,16,17)
SMILESCCCC(C)C1(C(=O)NC(=O)NC1=O)CC=C

Synonyms

  • Seconal
  • Quinalbarbitone
  • Reds
  • Red devils
Pharmacodynamics & Biochemistry

Secobarbital (Seconal, known in the UK as quinalbarbitone) is a short-acting barbiturate. Like the others it is a positive allosteric modulator of the GABA-A receptor, binding the barbiturate site to prolong GABA-evoked chloride-channel opening and, at higher concentrations, opening the channel directly: giving the characteristic barbiturate lack of any ceiling on sedation and respiratory depression. Its quick onset and short duration made it a popular sleeping pill: taken orally it is well absorbed and metabolised in the liver, with a half-life of roughly 15–40 hours. That fast, strong hypnotic effect also made it one of the most heavily misused barbiturates. Today its main remaining use is in physician-assisted dying, where a large oral dose of secobarbital is a standard agent: a stark illustration of how narrow its safety margin is.

Biological targets

  • GABA-A
Pharmacokinetics
BioavailabilityOral, well absorbed
TmaxNot reported
Half-life≈15–40 h
VdNot reported
Protein binding≈45–60%
MetabolismHepatic
ExcretionRenal
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.

125 mg/kg (rat, oral)

Secobarbital shares the barbiturate hazards: a low therapeutic index and no ceiling on respiratory depression, so a hypnotic dose and a fatal dose are dangerously close, and closer still with tolerance or when combined with alcohol, opioids or benzodiazepines. It was historically a common agent of both accidental and intentional fatal overdose. There is no specific antidote (flumazenil does not reverse barbiturates). Overdose care is supportive. It has a high potential for misuse and dependence, and abrupt withdrawal after regular use is dangerous: a syndrome resembling severe alcohol withdrawal (agitation, tremor, seizures, delirium) that can be fatal and needs a slow taper. Its reliable lethality is the reason it is used in physician-assisted dying.[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 Additive, potentially fatal respiratory depression.[2]
Drugs cleared by induced liver enzymes (warfarin, oral contraceptives, many antiepileptics, corticosteroids) Hepatic enzyme induction can reduce the effect of drugs such as warfarin and oral contraceptives.[2]

Contraindications

Significant respiratory depression or acute severe asthma severe respiratory depression or respiratory disease.[2]
Acute intermittent or related porphyria[2]
Kidney or liver impairment severe hepatic impairment.[2]
Combining with alcohol or other CNS depressants[2]
Known hypersensitivity to the drug barbiturate hypersensitivity.[2]
Usage & Context
  • A short-acting barbiturate (Seconal, UK quinalbarbitone) formerly prescribed as a hypnotic for insomnia and for preoperative sedation, now little used for those purposes.
  • Its main current use is in physician-assisted dying (a large oral dose).
  • Widely misused recreationally in the 1960s–1980s under street names such as 'reds' and 'red devils'.
Sources & Evidence

Further Information