Pentobarbital

5-Ethyl-5-(1-methylbutyl)-2,4,6(1H,3H,5H)-pyrimidinetrione

Pentobarbitone, Nembutal, Yellow Jackets

Psychoactive Class

Depressant Sedative Anticonvulsant Anxiolytic Muscle Relaxant GABAergic

Chemical Class

Pentobarbital is a short-acting barbiturate¹ that produces potent sedative, hypnotic, anxiolytic, muscle relaxant, and amnesic effects. It is used medically for the short-term treatment of insomnia,¹ as an emergency anticonvulsant,¹ and to induce medical comas.² Pentobarbital acts on GABA-A receptors at a distinct allosteric site from benzodiazepines² and is characterized by a relatively prompt onset of action. It is classified as habit-forming¹ and is internationally scheduled as a controlled substance.²

Dosage & Duration

Dosage

Threshold25-25 mg

Light50-100 mg

Moderate100-200 mg

Strong200-300 mg

Heavy200-300 mg

Bioavailability

70-90%

Duration

Onset15-60 minutes

Peak1-3 hours

Offset1-2 hours

After Effects1-36 hours

Total4-6 hours

Half-life

5-50 hours

Subjective Effects

The experience is dominated by heavy central nervous system depression, producing drowsiness, relief of tension and nervousness, and an intoxication broadly comparable to alcohol in character. Unlike opioids, pentobarbital provides little pain relief, and its use in the presence of significant pain can paradoxically result in excitation rather than calm. As the dose climbs, coordination, speech, and judgment deteriorate progressively, and at overdose levels the state shades into stupor, coma, and dangerously shallow breathing.

Physical

The body feels heavy, relaxed, and sedated, with incoordination and a staggering gait emerging as doses increase. Breathing becomes shallow at high doses, which is the primary driver of its overdose lethality.

Dangerous

Impairment

Sedation

Muscle relaxation

Cognitive

The headspace is slowed and clouded, with sluggish thinking, impaired judgment, and a marked reduction in anxiety and tension. Recall of the period under the drug's influence becomes unreliable at higher doses.

Suppressions

Disinhibition

Reagent Testing

Loading reagent data

Expected colorimetric results are being prepared.

Pharmacology

Pharmacodynamics

Pentobarbital acts primarily as a positive allosteric modulator of the GABA-A receptor, binding at the barbiturate site to prolong the duration of chloride ion channel opening.³¹ At higher concentrations, it is capable of directly activating the channel in the absence of GABA.³⁴ This potentiation of GABAergic inhibitory tone is associated with marked decreases in GABA-sensitive neuronal calcium conductance. Pentobarbital also directly inhibits excitatory AMPA-type glutamate receptors, suppressing glutamatergic neurotransmission,³⁵ and acts as an antagonist at NMDA receptors, kainate receptors, and neuronal nicotinic acetylcholine receptors (α4 and α7 subunits).³

Pharmacokinetics

Pentobarbital undergoes first-pass metabolism in the liver and possibly the intestines via the hepatic microsomal enzyme system, with subsequent renal excretion.¹² Oral bioavailability is approximately 70–90%, with 45–60% protein binding. The elimination half-life is dose-dependent, ranging from 5 to 50 hours.⁶¹

Metabolitesnone documented yet

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-BenzodiazepineAbacavirAbaloparatideAbataceptAbemaciclib

TripSit

Tolerance

Full Tolerance

Tolerance to the sedative-hypnotic effects develops after prolonged use. Clinical observations indicate that pentobarbital may lose its effectiveness for sleep induction by the second week of continued administration.

Cross Tolerance

Barbiturates

Baseline Reset

The exact duration required for tolerance to return to baseline is unknown.

Harm Potential

Addiction & Dependence

Psychological

Extremely High

Pentobarbital is deemed extremely psychologically addictive, with compulsive redosing commonly reported.¹ Short-acting barbiturates carry particularly high abuse potential, and the substance was widely abused beginning in the late 1930s.⁷

Physical

Extremely High

Pentobarbital produces severe physical dependence with chronic use.¹ Barbiturate withdrawal is medically serious and can cause a life-threatening syndrome including seizures, psychosis, and death with abrupt discontinuation.¹

Toxicity

Respiratory

Respiratory depression is the primary acute toxicity and can progress to respiratory arrest and death, particularly at higher doses or when combined with other CNS depressants.¹⁸

Carcinogenicity

Possible

Studies have linked barbiturate use with the development of cancer,⁹¹⁰ though phenobarbital has been particularly implicated;¹¹ evidence specific to pentobarbital is limited.

Psychosis Risk

Psychosis may occur as part of the life-threatening barbiturate withdrawal syndrome in dependent individuals.¹⁸ During intoxication, delusions of sobriety are reported at heavy doses, representing impaired reality testing rather than true psychosis.

Seizure Risk

Pentobarbital has anticonvulsant properties and suppresses seizures during use. However, abrupt discontinuation in dependent individuals may cause potentially fatal seizures as part of the withdrawal syndrome.¹⁸ Drugs that lower seizure threshold should be avoided during withdrawal.

History & Culture

Discovery and Development

Pentobarbital was developed by chemists Ernest H. Volwiler and Donalee L. Tabern at Abbott Laboratories in 1930.⁷ That same year, physician John S. Lundy began clinical use of the compound and coined the brand name Nembutal, an amalgamation derived from the…

Legality

International

UN Convention on Psychotropic Substances 1971 (Schedule III)

By Country

United StatesSchedule II

Controlled under the Controlled Substances Act.²³ Classified as having high potential for abuse but with currently accepted medical use.¹ Approved for short-term treatment of insomnia and widely used in veterinary medicine. Available by prescription in injectable formulations.

CanadaSchedule IV CDSA

Controlled under the Controlled Drugs and Substances Act.²⁰ Available for legitimate medical use with appropriate authorization. Historically marketed in combination products.

RussiaSchedule II

Controlled substance under federal narcotics legislation. Subject to strict regulation with limited availability for medical purposes.

United KingdomClass B

Controlled under the Misuse of Drugs Act 1971.²² Unauthorized possession, supply, and production carry criminal penalties, though less severe than Class A substances.

AustraliaSchedule 8

Controlled drug under Australian scheduling. Schedule 8 substances are available for therapeutic use but require strict prescribing and record-keeping requirements due to abuse potential.

GermanyAnlage III BtMG

Listed in Anlage III of the Betäubungsmittelgesetz (Narcotics Act),²¹ indicating it is a marketable narcotic with recognized medical applications. Prescriptions require a special narcotic prescription form (Betäubungsmittelrezept).

SwitzerlandVerzeichnis B

Specifically named controlled substance under Verzeichnis B of Swiss narcotics legislation. Medicinal use is permitted with appropriate medical authorization.

References

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Citations

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