GBL (Gamma-Butyrolactone)
Definition
A prodrug of GHB spontaneously hydrolysed by blood paraoxonase-1 to GHB within minutes. An industrial solvent; scheduled as Class C in the UK since 2009. May be detected in blood drawn very shortly after ingestion before full conversion to GHB.
- Relationship to GHB
- Prodrug, converts to GHB in the body
- Conversion enzyme
- Blood paraoxonase-1
- Conversion speed
- Within minutes of ingestion
- UK legal status
- Class C controlled substance since 2009
- Other use
- Industrial solvent
Common questions
Why would a toxicologist test for GBL specifically rather than only GHB?+
Because GBL hydrolyses to GHB within minutes, a blood sample drawn very soon after ingestion may still contain detectable GBL alongside GHB, and identifying GBL directly can help establish the route and recency of exposure rather than relying on GHB levels alone.
Does GBL's status as an industrial solvent complicate death or overdose investigations?+
Yes, because GBL has legitimate industrial uses such as a paint stripper and cleaning solvent, its presence in a scene does not by itself indicate recreational or predatory drug use, so investigators correlate scene context with the toxicology and circumstances of exposure.
Why is GBL controlled separately from GHB in some jurisdictions?+
Because GBL was historically sold as an unregulated precursor that converts to GHB after ingestion, allowing it to circumvent GHB-specific drug laws, so regulators such as the UK moved to schedule GBL itself once this loophole became apparent.
Related terms
- 7-Aminoflunitrazepam
- The primary urinary metabolite of flunitrazepam (Rohypnol), detected by LC-MS/MS in urine for up to 72 hours post-ingestion. The target analyte for...
- DFSA (Drug-Facilitated Sexual Assault)
- Sexual assault in which a substance is administered without the victim's consent to induce sedation, incapacitation, or amnesia. Most common substances in...
- Endogenous GHB Threshold
- Normal human blood GHB is 0.5-4 mg/L; urine 1-10 mg/L. Post-mortem fermentation can raise values to 20-50 mg/L. Forensic toxicologists typically use...
- Etizolam
- A thienodiazepine (thiophene ring instead of benzene ring fused to the diazepine) with GABA-A modulation pharmacology equivalent to classical benzodiazepines. Approved in...
- Flubromazolam
- A potent triazolo-benzodiazepine (active at 0.125-1 mg), not internationally scheduled, appearing in DFSA and overdose casework. Not cross-reactive with standard BZD immunoassays....
- GABA-a Receptor
- The main inhibitory ligand-gated ion channel in the CNS; a pentameric alpha-beta-gamma subunit complex that opens its central chloride channel when GABA...
- GHB (Gamma-Hydroxybutyric Acid)
- An endogenous GABA metabolite and short-chain fatty acid; exogenous doses of 1-3 g produce sedation, euphoria, and amnesia. Blood half-life ~20-30 min;...
- Phenobarbital
- A long-acting barbiturate (half-life 80-120 h) listed on the WHO Essential Medicines List as a first-line antiepileptic; Schedule IV under the UN...
- Positive Allosteric Modulation
- Mechanism by which benzodiazepines enhance GABA-A function: they increase the frequency of chloride channel opening in response to GABA without directly activating...