GBL

GBL/GHB produces bradycardia at pharmacological doses. Individuals with pre-existing cardiac conduction disorders face elevated risk of hemodynamically significant bradycardia or asystole. The first UK GBL fatality involved asystole.

asthma, COPD, obstructive sleep apnea

GBL produces dose-dependent respiratory depression. Individuals with pre-existing respiratory impairment have reduced physiological reserve, increasing vulnerability to hypoxia and respiratory arrest at doses that might be tolerated by individuals with normal respiratory function.

The relationship between GBL/GHB and seizure threshold is bidirectional: GHB can suppress seizure activity at some doses but the withdrawal syndrome produces seizures in approximately 7% of episodes. Individuals with seizure history face unpredictable risk both during use and during any withdrawal period.

GBL's rapid onset, short duration, and high compulsive redosing urge create an exceptionally reinforcing cycle. Individuals with prior substance dependence are at elevated risk of developing GBL dependence, which progresses more rapidly than alcohol or benzodiazepine dependence.

No human safety data exist for GBL or GHB use during pregnancy or breastfeeding. Given the compound's CNS and respiratory depressant effects and the absence of any reproductive toxicology data, this contraindication is precautionary.

ketamine, PCP, methoxetamine, 2-fluorodeschloroketamine, rolicyclidine

Ketamine and other dissociatives produce additive to synergistic CNS depression when combined with GBL. The combination is classified as lethal due to risk of deep unconsciousness with compromised airway reflexes.

Alcohol combined with GBL produces synergistic CNS and respiratory depression that is classified as a lethal combination across multiple clinical reviews. Even moderate alcohol intake markedly elevates risk of coma, respiratory arrest, and death.

heroin, morphine, oxycodone, fentanyl, methadone, codeine, tramadol, buprenorphine, hydromorphone, hydrocodone

All opioids produce lethal synergistic respiratory depression when combined with GBL. This applies across the full opioid class including partial agonists (buprenorphine) and atypical opioids (tramadol). The combination is unambiguously classified as lethal.

benzodiazepines, barbiturates, sedating antihistamines, antipsychotics, muscle relaxants, prescription sleep aids

All CNS depressant medications markedly enhance sedation and respiratory depression when combined with GBL. Benzodiazepines in particular reduce protective airway reflexes. Baclofen produces excessive GABA-B agonism at recreational doses, though it is used therapeutically in supervised withdrawal management.