Tox In Focus

Focused Clinical Reference

Vol. 29 · Barbiturates · July 2026

Drug Quick Reference

Drug Class / Mechanism

GABA-A modulators (non-specific)

Sedative / hypnotic / anticonvulsant

Street Names

'Barbs', 'downers'

'Reds' (secobarbital)

Routes of Administration

Oral (therapeutic)

Misuse oral or injection

Commonly Detected With

Opioids, alcohol, benzodiazepines · Butalbital combos (caffeine, APAP)

Metabolism

Hepatic microsomal; renal hydroxylated products

Phenobarbital: potent enzyme inducer

Window of Detection

Urine: days to several weeks

Longest for long-acting phenobarbital

Control Status

DEA controlled (Schedule II-IV by agent)

BARBITURATES

Phenobarbital, butalbital, and a withdrawal that can be lethal

Barbiturates are GABAergic sedative-hypnotics and anticonvulsants largely replaced by safer agents, but phenobarbital (epilepsy, alcohol withdrawal) and butalbital (headache combination products) remain in use. LC-MS/MS identifies specific agents; phenobarbital is a potent enzyme inducer that alters the metabolism of many co-prescribed drugs.¹

Why This Matters Now

Barbiturates have a narrow therapeutic index and dangerous withdrawal: abrupt discontinuation after sustained use can cause seizures and delirium and can be fatal, similar to alcohol and benzodiazepine withdrawal. Phenobarbital's enzyme induction can also lower levels of co-prescribed medications, including other antiepileptics.²

⚠ Do not stop barbiturates abruptly after chronic use; withdrawal can progress to seizures and death. Consider phenobarbital's enzyme induction when a co-prescribed drug is unexpectedly subtherapeutic.

Clinical Presentation

INTOXICATION

Sedation, slurred speech, ataxia

Respiratory depression

Hypotension

Reduced level of consciousness

Coma (overdose; narrow margin)

WITHDRAWAL

Anxiety, agitation, insomnia

Tremor

Autonomic hyperactivity

Seizures (life-threatening)

Delirium

Important: Barbiturate overdose causes respiratory depression with a narrow margin of safety, and withdrawal can be life-threatening. Combined with opioids, alcohol, or benzodiazepines, the respiratory-depression risk is additive.

UDT Considerations

LC-MS/MS distinguishes butalbital, secobarbital, pentobarbital, and phenobarbital, which immunoassay cannot separate. Detection windows vary widely by agent, from a few days to several weeks (longest for long-acting phenobarbital). Alkalinizing the urine increases phenobarbital excretion, which can affect measured levels.³

Clinical Guidance

Order specific LC-MS/MS to identify the barbiturate; immunoassay does not distinguish agents.¹
Never stop chronic barbiturates abruptly; taper to avoid life-threatening withdrawal.
Account for phenobarbital enzyme induction lowering co-prescribed drug levels.²
Assess additive sedation with opioids, alcohol, and benzodiazepines.
Interpret prolonged phenobarbital detection in the context of its long half-life.

Point-of-Care Testing Availability

Available strips

Barbiturate immunoassays exist but vary in sensitivity by agent.

Clinical use

LC-MS/MS identifies specific barbiturates (butalbital, secobarbital, pentobarbital, phenobarbital).

Limitations

Phenobarbital induces CYP enzymes, altering other drug levels.

BARBITURATES | Clinical & Program Guidance

Tox In Focus Vol. 29 · July 2026 · Page 2 of 2

Interpreting the Test Result

▲ If Testing Is Positive

Confirms recent use. Detection indicates use within the (agent-dependent) window; levels do not confirm dose.

Identify the specific agent. LC-MS/MS separates butalbital, secobarbital, pentobarbital, and phenobarbital.

Phenobarbital persists. Its long half-life means detection can extend for weeks after last use.

▼ If Testing Is Negative or Not Done

Agent-dependent window. Short-acting agents clear in days; a negative may reflect timing.

Timing and cutoff. Absence may reflect timing of last use, dose, or levels below the cutoff.

Immunoassay varies. Sensitivity differs by barbiturate; confirm by LC-MS/MS.

Barbiturates Tested: Duration and Use

Barbiturate	Duration class	Typical use / note
Butalbital	Short to intermediate	Headache combinations (Fioricet, Fiorinal)
Secobarbital	Short-acting	Hypnotic; preanesthetic
Pentobarbital	Short-acting	Sedative; procedural
Phenobarbital	Long-acting	Epilepsy; alcohol withdrawal; potent CYP inducer

Detection windows lengthen with duration of action; phenobarbital persists longest and induces CYP enzymes.

Key References

Skibiski J, Abdijadid S. Barbiturates. StatPearls. 2021.
Lewis CB, Adams N. Phenobarbital. StatPearls. 2021.
Baselt RC. Disposition of Toxic Drugs and Chemicals in Man. 8th ed. Biomedical Publications; 2008.

DISCLAIMER: This document is intended for clinical reference and educational purposes only. It does not constitute medical, legal, or professional advice and should not replace independent clinical or programmatic judgment. Content reflects published data available at time of preparation. ToxiPharm LLC makes no warranties regarding completeness or applicability in all settings. | © 2026 ToxiPharm LLC | toxipharm.org