Gamma-butyrolactone

γ-butyrolactone is a hygroscopic colorless oily liquid with a weak characteristic odor and is soluble in water. gamma-Butyrolactone is a common solvent and reagent in chemistry and is used as an aroma compound, as a stain remover, as a paint stripper, and as a solvent in some wet aluminum electrolytic capacitors.

Occurrence
The compound gamma-butyrolactone (GBL) was found in extracts from samples of unadulterated wines. This finding indicates that GBL is a naturally occurring component in some wines and may be present in similar products. The concentration detected was approximately 5 μg/mL and was easily observed using a simple extraction technique followed by GC/MS analysis.

Preparation
gamma-Butyrolactone can be synthesized from gamma-hydroxybutyric acid by removal of water or by distillation from such a mixture. It may also be obtained via oxidation of tetrahydrofuran (THF). One such process, which affords GBL in yields of up to 80%, utilises bromine generated in situ from an aqueous solution of sodium bromate and potassium hydrogen sulfate.

Chemistry
gamma-Butyrolactone is a lactone. It is hydrolyzed under basic conditions, for example in a sodium hydroxide solution into sodium gamma-hydroxybutyrate, the sodium salt of gamma-hydroxybutyric acid. Under acidic conditions it forms an equilibrium mixture of both compounds.

Pharmacology
GBL is not active in its own right, its mechanism of action stems from its identity as a prodrug of gamma-hydroxybutyrate.

The hypnotic effect of GHB is enhanced by combination with alcohol. A 2003 rat study showed that GBL in combination with ethanol showed a potentiated hypnotic effect, as the sleep-timing measure was longer than both of the individual components combined.

Pharmacokinetics
Gamma-butyrolactone is rapidly converted into GHB by lactamase enzymes found in the blood. GBL is more lipophilic (fat soluble) than GHB, and so is absorbed faster and has higher bioavailability; the paradox is that this can mean that GBL has a faster onset of effects than GHB itself, even though it is a prodrug. The levels of lactamase enzyme can vary between individuals, and GBL is not active in its own right, so people who have never tried GBL before may have delayed or fewer effects than expected; however, once someone has taken GBL a few times, the production of lactamase enzymes is increased and he/she will feel the effects like normal.

Because of these pharmacokinetic differences, 1,4-B tends to be slightly less potent, slower to take effect but longer-acting than GHB, whereas GBL tends to be more potent and faster-acting than GHB, and has around the same duration.

Recreational use
GBL is a prodrug of GHB. To bypass GHB restriction laws, home synthesis kits were introduced to transform GBL and/or 1,4-butanediol into GHB. GBL can also be used as a recreational drug by itself.

GBL overdose can cause severe sickness, coma and death.

Metabolism takes place in stomach and blood plasma. GBL is longer acting and has a shorter onset than GHB. Otherwise, effects are similar to GHB, although weight for weight it is significantly more powerful, meaning dosage must be lowered accordingly. If ingested undiluted through the oral route, GBL can irritate innards. It is possible for oral ingestion of GBL to cause nausea and other similar problems, possibly more so than with GHB.

Dose
A milliliter of pure GBL metabolizes to roughly a gram of GHB, so doses are measured in the single milliliter range, either taken all at once or sipped over the course of a night.

Restricting the use of GBL
Although GBL is an unclassified drug in the United Kingdom, risk to people's lives is being recognised on the London Gay Scene, where use is more prevalent than other parts of the country. At the end of 2006, a campaign began to reduce the number of people using GBL in the area. The effects of this campaign are yet to be seen.