GBL (gamma-butyrolactone) and BDO (1,4-butanediol) are GHB precursors, i.e. they are converted by the body into GHB. GHB is closely related to endogenous gamma-aminobutyric acid (GABA) and activates certain GABA receptors. GABA is the most important inhibitory neurotransmitter in the brain and regulates sleep-wake cycles, memory functions and growth hormones, among other things. GHB/GBL/BDO can have stimulating as well as relaxing and calming effects, depending on the phase of action, dosage and individual metabolism. In medicine, GHB is used in the treatment of narcolepsy and I some countries also against the withdrawal syndrome in alcohol dependence.
If you or someone else needs urgent help after taking drugs or alcohol, call an ambulance on 144. Tell the emergency responders everything you know.
It could save lives.