Introduction Data on emergency interventions in poisonings are scarce. Objective To determine the effectiveness of antidote therapy in acute poisoning-related emergency medical services (EMS) interventions. Methods A prospective observational study included all poisoning-related intervention cases over 3 years (1999-2001) in the Celje region, Slovenia, covering 125,000 inhabitants. Data were recorded on an EMS form. Results Psychoactive agents were present in 56.5% out of 244 poisoning-related EMS interventions. Prescription drugs were a cause of intoxication in 93 (39.2%) cases alone or in combination with alcohol or illegal drugs. More than one fifth of poisonings were due to the use of illegal drugs in 52 (21.9%) cases, 43 (18.1%) out of them heroin related. At the time of EMS arrival, more patients who ingested illegal drugs were in coma or comatose than the rest. 24 (45.3%) vs. 32 (17.3%) of poisoned patients were in coma (p<0.001). Glasgow Coma Scale (GCS) at the first contact was lower in patients who ingested illegal drugs than in the remaining patients (9.0 vs. 11.6, p=0.001). In 23.2% of the cases, an antidote was administered. In 29(12.2%) naloxone and in 16(6.7%) flumazenil was administered. Mean GCS after intervention was higher in all cases but significantly higher in illegal drug cases, 13.4 vs. 12.2 (p=0.001), with a mean positive change in GCS of 4.5 vs. 0.6 (p<0.001). In illegal drug users, mean change after antidote administration was 8.2 vs. 0.5 without antidote administration (p<0.001). Conclusion High rate of successful antidote use during the intervention indicated the importance of good EMS protocols and the presence of a skilled doctor in the EMS team.