GHB / GBL

GHB is an endogenous GABA metabolite and the most narrow-therapeutic-window CNS depressant in common use — recreational dose 1.5-2.5 g, unconscious at 3-4 g, respiratory arrest at 7+ g. Sodium oxybate (Xyrem/Xywav/Lumryz) is medical-grade GHB with A-tier evidence for narcolepsy with cataplexy and idiopathic hypersomnia under a restricted-distribution REMS program ($177K-212K/yr cash price). Outside that envelope, GHB/GBL produces severe physical dependence within weeks at q2-4hr dosing, withdrawal that mirrors or exceeds severe alcohol withdrawal (delirium >50%, ICU 20-31%, benzodiazepine-resistant), and a death profile dominated by alcohol co-ingestion (>90% of GHB-related deaths in Australia 2001-2023 involved other substances). GBL is GHB's lipophilic prodrug — same active drug, faster onset, sold as industrial solvent, banned in UK/EU. SKIP-PERMANENT, HIGH confidence, for every archetype. No biohacker use case justifies the dosing-error fatality risk + dependence pharmacology. Daridorexant covers sleep architecture without GHB's lethality; SSRIs/Selank cover anxiolysis; modafinil covers wake-promotion in narcolepsy at first-line.

GHB is 4-hydroxybutanoic acid — a 4-carbon short-chain fatty acid that is endogenously synthesized in the human CNS from GABA via the SSADH-reverse pathway (GABA → succinic semialdehyde → GHB via SSADH operating in reverse direction in some neurons; also via aldehyde reductase). Endogenous tissue concentrations sit in the 1-4 µM range across cortex, hippocampus, hypothalamus, thalamus — i.e., GHB is a normal constituent of brain biochemistry, not a foreign molecule. Pharmacological doses are 100-1000× higher and engage receptors that endogenous concentrations do not.

Pharmacological GHB acts at two distinct receptor systems:

1. GABA-B receptor (orthosteric agonist, low-affinity). EC50 in the millimolar range (compare baclofen Ki ~6 µM, phenibut Ki ~92 µM). GABA-B is a Gi/o-coupled metabotropic receptor — activation closes presynaptic N- and P/Q-type voltage-gated calcium channels (reducing glutamate release) and opens postsynaptic G-protein-coupled inwardly rectifying K⁺ channels (GIRK), hyperpolarizing the neuron. Net effect: presynaptic + postsynaptic inhibition of excitatory transmission. This is the receptor that drives GHB's sedation, sleep-architecture effects, anxiolysis, ataxia at high doses, respiratory depression, and the cataplexy-suppressing therapeutic effect in narcolepsy. Knockout studies (GABBR1-deficient mice, PMID 14656321) confirm that virtually all of GHB's behavioral and physiological effects vanish in animals lacking the GABA-B receptor — making GABA-B the dominant pharmacological target despite the lower affinity, simply because pharmacological concentrations exceed it.

2. GHB receptor (GHBR / GPR172A) — high-affinity, distinct excitatory GPCR. Originally identified as a discrete binding site by ³H-GHB autoradiography in the 1980s; molecularly cloned as GPR172A. Micromolar affinity — engaged at endogenous concentrations and at low pharmacological doses below the GABA-B threshold. Function still being characterized; the GHBR appears to be excitatory (paradoxically — couples to Gq-like signaling in some cell systems), and may mediate the biphasic dose-response phenomena GHB users report (low doses are mildly stimulating + euphoric; high doses are sedating + anesthetic). The GHBR's existence is why GHB is classed as having its own neurotransmitter-like signaling system on top of being a GABA-B agonist. Clinical relevance is debated; the dominant clinical effects ride on GABA-B, not GHBR.

3. GABA-A α4βδ extrasynaptic receptors — debated. A 2012 PNAS paper (PMID — Absalom et al.) proposed GHB as a high-affinity agonist at extrasynaptic α4βδ GABA-A receptors. A 2013 PLOS One paper (Connelly et al.) explicitly contested this finding — direct electrophysiology showed no agonist activity at extrasynaptic GABA-A in their preparation. Net assessment: if GHB has any GABA-A activity, it's at extrasynaptic tonic-current receptors and is likely minor relative to GABA-B + GHBR effects. Treat as unsettled.

Plain English mechanism: GHB is a tiny GABA-derived molecule that your brain already makes. Take pharmacological amounts and it does two things — (a) weakly but dose-dependently activates the same metabotropic GABA-B receptor as baclofen and phenibut, producing sedation, calm, slow-wave sleep enhancement, and at higher doses unconsciousness + respiratory depression; (b) more strongly activates a separate "GHB receptor" that is excitatory and probably accounts for the low-dose sociable + euphoric phase before the GABA-B sedation kicks in. The biphasic dose-response (stimulating-then-sedating, with the transition over a tiny dose increment) is the clinically dangerous feature — there is no dose tier that produces "more relaxation" without also producing "now you're unconscious."

GBL (gamma-butyrolactone) — the lactone prodrug: GBL is the cyclic ester (lactone) form of GHB — the same 4-carbon backbone with an internal cyclic bond instead of a hydroxyl + carboxylate. Pharmacologically inactive itself but rapidly hydrolyzed to GHB by serum and hepatic lactonases (especially paraoxonase / PON1) within minutes of absorption. Because GBL is lipophilic and uncharged, it crosses GI membranes and the blood-brain barrier faster than GHB sodium salt. Onset 5-15 min for GBL vs 15-30 min for GHB; effective dose ~half by mass because of faster, more complete absorption (~2 mL GBL ≈ ~3-4 g GHB sodium salt subjective potency). This faster onset is what makes GBL more dangerous in practice — users frequently mistake the slower GHB onset for inactivity and re-dose, but with GBL the same redose pattern produces overdose because the original dose has already absorbed.

1,4-butanediol (1,4-BD) — separate prodrug, oxidized via alcohol dehydrogenase + aldehyde dehydrogenase (the same enzymes that handle ethanol) to GHB. Coingestion with alcohol dramatically extends 1,4-BD's effects because ethanol competes for ADH, slowing 1,4-BD → GHB conversion. Treated as GHB-equivalent in clinical practice and law.

Pharmacokinetics:

• Half-life: 30-50 minutes (extremely short; saturable kinetics — at high doses elimination shifts from first-order to zero-order, prolonging duration unpredictably).
• Onset: 15-30 min PO (GHB sodium salt), 5-15 min PO (GBL).
• Peak: 30-60 min.
• Duration of effects: 1.5-4 hours single dose; longer at high doses due to saturable elimination.
• Volume of distribution: small (~0.4 L/kg) — water-soluble.
• Elimination: ~95% hepatic metabolism (oxidation back to succinic semialdehyde → succinate → TCA cycle); <5% renal excretion unchanged. CO₂ exhalation accounts for substantial elimination — the body literally breathes it out as the carbon backbone enters the TCA cycle.
• Detection: Urine detection window ~12 hours; plasma ~6-8 hours. Standard immunoassay drug screens DO NOT detect GHB — LC-MS or GC-MS required. Endogenous concentrations create assay-cutoff complexities (must distinguish exogenous from endogenous via concentration thresholds, typically >5-10 mg/L plasma for exogenous determination).

Why the therapeutic window is narrow: the half-life is short (30-50 min) and elimination is saturable (Michaelis-Menten kinetics — at recreational doses elimination becomes rate-limited). Net effect: small dose increases produce disproportionately large duration + peak effects. Going from 2 g to 4 g doesn't just double the effect — it more than quadruples the AUC because elimination is already saturated at lower doses. This is why "I'll just take a little more" is a fatal pattern.