GHB and alcohol strengthen each other's sedating effect and both suppress breathing, so a small amount of GHB can already be too much. Trimbos warns that the person can fall into a coma and even die (DRUGSinfo, combinations). Its general advice is short: never combine GHB with alcohol, other drugs or medicines.
Why depressants add up
GHB, alcohol, sleeping pills, benzodiazepines and opioids all slow down the brain systems that keep you awake and breathing. Taken together, the effects stack. The Nationale Drug Monitor names alcohol, opioids and sleeping and calming medicines, and says the combination suppresses breathing even more and raises the chance of death (Nationale Drug Monitor).
A forensic review calls GHB a particularly troublesome drug partly because of its risk of adverse interaction with other sedatives (Busardò and Jones 2015). Research in rats found a synergistic effect of GHB and alcohol given together, more than the two effects added up (Metabolites 2023). That was an animal study, but it fits what emergency services see.
There is a chemical twist for 1,4-butanediol, one of the liquids sold as G. It needs alcohol dehydrogenase, the same enzyme that breaks down alcohol, to turn into GHB (Felmlee et al. 2021). With alcohol in the body the two compete for that enzyme, which makes the timing of the effect even harder to predict.
Combinations at a glance
| Combined with | What happens | Source |
|---|---|---|
| Alcohol | sedation adds up, breathing slows, coma possible | DRUGSinfo |
| Sleeping pills, benzodiazepines | higher risk that breathing stops | DRUGSinfo |
| Opioids | breathing slowed even further, higher chance of death | Nationale Drug Monitor |
| Ketamine | suppressed breathing and unconsciousness, more nausea and vomiting, choking risk | DRUGSinfo, ketamine |
| Cocaine, speed, ecstasy | the stimulant hides the drowsiness; when it wears off, the person can suddenly go out | DRUGSinfo |
| 4-FA | the same masking effect, more chance of overdose and going out | Drugs & Uitgaan |
Stimulants hide the warning signs
With cocaine, speed or ecstasy in the body, someone notices less of the sedating effect of GHB. Trimbos explains the result: the user takes more GHB sooner, and when the stimulant wears off while a lot of GHB is still active, they can suddenly lose consciousness (DRUGSinfo, combinations). Ecstasy with GHB also lowers inhibitions further, and Trimbos' nightlife site notes that the combination may make a coma deeper and longer (Drugs & Uitgaan, combinations).
That is why a person who seemed lively at the party can be out on the way home.
What Dutch emergency data show
In the Trimbos Monitor Drugsincidenten for 2024, 46% of GHB incidents (483) involved more than one drug. GHB was most often combined with amphetamine (28%), cocaine (26%), ecstasy (25%), 3-MMC (22%), cannabis (12%) and ketamine (11%). Among the incidents with GHB as the only drug, alcohol was also recorded in 19% (Monitor Drugsincidenten 2024).
The monitor covers only the ambulance services, first-aid posts and hospitals that take part, so these are shares of reported incidents and no estimate of total risk.
What this means in practice
- "I only had a few drinks" is a reason for more caution around anyone who has taken GHB, never less.
- Medicines count. Sleeping pills, anxiety medication and strong painkillers are downers too.
- After a stimulant, the drowsiness can arrive late. Stay in company for the rest of the night.
- If someone becomes very sleepy or cannot be woken, go to someone is out and call 112.
A test cannot make a combination safer. It can show whether a bottle contains GHB at all, so that nobody unknowingly adds GBL or something else to a night that already includes alcohol: testing a liquid.
