Discussion
The incidence of drug and alcohol poisonings treated at OAEOC increased between 2019 and 2023, though the rise was substantially smaller than that observed in the period 2008–2018 (Figure 1) (10–12) . After a decline in 2020 and 2021, a total of 4138 cases were recorded in 2023, just slightly higher than the 4021 cases reported for 2018 (12) . Ethanol, heroin and benzodiazepines remained the most frequently involved substances, consistent with findings from Trondheim (12, 13) .
Over the past decade, the incidence of heroin poisonings has fluctuated within a stable range, whereas the increased incidence of unspecified opioid poisonings observed in 2017–2018 remained high throughout 2019–2023 (12) . A substantial proportion of these cases involved long-acting opioids (20) . Naloxone, an opioid antagonist, has a relatively short duration of action, and repeated administration may be necessary within 1–2 hours. This highlights the importance of a two-hour observation period following opioid antagonist treatment (21) . In light of the record number of deaths from novel synthetic opioids in Norway in 2023 (5, 6) and the rising number of fatal overdoses linked to prescribed opioids (22) , these trends are a cause for concern.
We observed a major increase in cocaine poisonings, rising from 163 cases in 2019 to 432 in 2023, with most cases occurring among adolescents and young adults. Reports from Norway indicate that cocaine use has increased over the past five years, particularly in this age group (5) . Large seizures of cocaine suggest increased importation (23) , and wastewater analyses indicate rising consumption in Oslo (24) . Among upper secondary school pupils in Oslo, the proportion reporting cocaine use tripled between 2018 and 2023, to 17 % of male final-year pupils (25) . Increasing cocaine use among adolescents and young adults has been reported throughout Europe and corresponds with a simultaneous large rise in cocaine seizures (6) . Cocaine is implicated in approximately one fifth of drug-related deaths in Europe (6) , with myocardial infarction, arrhythmias and stroke representing the main risks (26) . Clinicians should therefore remain alert to the possibility that chest pain following cocaine use may indicate a coronary event, even in patients considered too young for coronary artery disease.
The number of ketamine poisoning cases increased from six in 2019 to 77 in 2023. While this magnitude is new for Oslo, it is in line with the increasingly frequent and larger ketamine seizures (23) . Rising prevalence and seizures are also reported in other parts of Europe and the United States (6, 27) . Ketamine, an anaesthetic also used recreationally, can cause agitation, dissociation, hallucinations and confusion in cases of acute intoxication, which are best managed with benzodiazepines (28) . Chronic ketamine use can lead to ulcerative cystitis (28) .
We found a marked increase in poisonings involving benzodiazepines in 2023, accompanied by a higher proportion of cases among adolescents and young adults. It remains unclear whether this reflects increased use of illicit benzodiazepines or misuse of prescribed benzodiazepines among patients treated for poisoning with other primary agents. No corresponding changes were observed in police seizures of benzodiazepines (23) .
The rise in the proportion of women in our data was due to an increase in the number of female cases, while the number of male cases remained stable. This increase was seen for nearly all substances, particularly MDMA. Among school pupils, the proportion of girls who reported alcohol intoxication during the past 12 months increased from 32 % in 2018 to 37 % in 2023, while the proportion of boys remained stable at 32 % (25) . However, survey data show no increase in the proportion of women who drank alcohol in the past year, nor in those who consumed more than six units on a single occasion in the same period (4) . Surveys also indicate a slight rise in cannabis use among women in general and among girls of school age (5, 25) . Taken together, these findings suggest an increase in psychoactive substance use among women, which may help explain the rising number of drug and alcohol poisonings among women. Across Europe, women account for roughly one quarter of people with serious problems related to illicit drug use, and our findings are consistent with this (29) . Notably, women made up 43 % of MDMA poisonings in our data, and as many as 61 % in 2023 – considerably higher than the 29 % reported in a European study covering 2013–2022 (30) .
The observed decline in drug and alcohol poisonings in 2020–2021 is likely attributable to the lockdowns during the COVID-19 pandemic. The incidence was markedly lower in months with a full lockdown, particularly for ethanol poisonings. Psychoactive substances are often consumed in social contexts, and the restrictions led to a shutdown of the hospitality sector and limited social contact. It is also possible that substance use shifted from public settings to private homes, reducing the likelihood of being found and brought in for treatment following intoxication.
Although reports from ambulance personnel and the police indicated increased GHB use due to heroin shortages, no corresponding rise in GHB poisonings was observed at OAEOC. GHB poisoning is often so severe that patients are transported directly to hospital by ambulance, so an increase may have gone unnoticed at OAEOC. However, no rise was observed at Oslo University Hospital either (K.E. Hovda, senior consultant, Department of Acute Medicine, personal communication, unpublished Euro-DEN data).
Excluding pure ethanol poisonings, the proportion of patients transferred from OAEOC to somatic hospitals declined from 18 % at the start of our previous study in 2014 (12) to 11 % at the end of the latest study in 2023. This could reflect a higher threshold for hospital transfer, although there have been no changes in the clinic's routines to suggest this. It is also possible that the threshold for presenting to the clinic with drug and alcohol poisoning has decreased (12) .
The proportion of patients leaving the clinic during treatment was markedly low in 2020–2021, possibly because staff had more time for follow-up due to reduced patient volumes during the pandemic lockdown.
Strengths and limitations
Strengths and limitations
Most patients with drug and alcohol poisoning in Oslo are treated at OAEOC, while the most severe cases are transported directly to hospital by ambulance. Some patients remain at the scene after receiving care from ambulance personnel and are therefore not included in our dataset (18) . In addition, there are fatal overdoses and cases where the health service is not involved at all. Although our findings do not provide a complete picture of the situation in Oslo, they are a strong indicator of the prevalence of different substances used in drug and alcohol poisonings. Given that our findings are consistent with a similar study from Trondheim and with national data on police seizures, they are likely generalisable to other urban settings in Norway (13, 23) . The large sample size reduces susceptibility to random variation, and combined with previous studies, provides a robust dataset spanning 2008 onwards (10–12) for monitoring trends over time.
Incidence rates are not an exact measure of drug and alcohol poisonings in the Oslo population, but they serve as a useful metric for monitoring trends over time. Although 30 % of patients with drug and alcohol poisoning are not Oslo residents (31) , population figures from Oslo local authority were used as the denominator for incidence calculations. Because drug and alcohol poisoning is extremely rare in children under 12, the at-risk population was defined as individuals aged ≥ 12 years.
Cases were identified through a retrospective review of OAEOC's presentation records, and were included if the patient was recorded with a condition suggestive of drug and alcohol poisoning. It is therefore likely that not all cases were captured.
We recorded the number of cases rather than individual patients. In two previous Norwegian studies, 14 % of patients were treated for more than one poisoning episode within a year (11) and 20 % within two years (13) , with 1 % and 2 %, respectively, experiencing more than five episodes. Given that our study spans a five-year period, the proportion of patients with more than one episode is expected to be slightly higher. Nonetheless, counting cases is appropriate for our purposes, as our primary interest is in identifying the substances likely to be implicated in drug and alcohol poisonings encountered in clinical practice.
Data were collected retrospectively from medical records. No routine toxicological testing was performed. Substance diagnosis was based on the treating doctor's clinical assessment, as documented in the medical record, drawing on information from patients and their companions, and the clinical presentation. Toxicological analyses indicate that patients generally report the substances they have taken, although some substances may be underreported when multiple substances are involved (32) .
Some inconsistencies in case inclusion and data recorded are likely, even though all ten medical students who collected the data were trained and supervised by the same person (last author).
Conclusion
Conclusion
The incidence of drug and alcohol poisonings treated at OAEOC increased between 2019 and 2023, with a temporary decline during the COVID-19 pandemic in 2020 and 2021. Poisonings involving cocaine and ketamine rose sharply, particularly among adolescents and young adults. Clinically, this highlights the importance of recognising that chest pain following cocaine use may indicate a coronary event, even in patients who would normally be considered too young for coronary artery disease, and that acute confusional states may be due to ketamine use.