To the best of our knowledge, this study was the first to investigate the poisoning patterns related to different drugs/substances before and after the COVID-19 pandemic. With the assessment of more than 13,000 patients, we found no difference between the demographic characteristics of the patients before and during the pandemic. In overall poisoning cases, while there was an increasing trend before the pandemic, there was a sudden drop in the first month of COVID-19. However, the trend slope was rising during the COVID-19 pandemic as well. Other main findings of the current study were: (1) there was a sudden decrease in the rates of all poisonings except ethanol and methanol, (2) the overall trend was rising for all poisonings other than methanol and cannabis, and (3) although all there was a sudden decrease in all poisoning admissions at the beginning of the pandemic, the proportion of ethanol and methanol poisonings had significant increases.

The COVID-19 pandemic had a profound impact on healthcare systems all around the world. These effects included decreased hospitalization from non-COVID-19 diseases and conditions and increased in-hospital mortality^20,21. For instance, in Spain, a decrease of 22% in non-COVID medical and 33% in surgical hospitalizations was observed during the first wave of the pandemic²². In another study conducted in the United States as well, a steep decline was observed in admissions other than COVID-19 during the first months of the pandemic²⁰. This was observed in several other studies as well^23–26. Similarly, we found a significant decrease in poisoning admissions at our center, mostly due to the allocation of available beds to patients with COVID-19.

The global use of alcohol has increased from 1990 to 2017 and the trend is still upward²⁷. The COVID-19 pandemic increased the rate of consumption and changed the patterns of using alcohol²⁸. Several surveys found higher alcohol consumption in the United States during the COVID-19 pandemic compared to 2019^29–32. In the report National Center for Health Statistics (NCHC) published in November 2022, they found a sharp increase in alcohol-related mortality with the emergence of COVID-19³³. Although the increase rate between 2000 and 2018 was about 7% in alcohol-related deaths, this was changed to 26% from 2019 to 2020 which can be the effect of the COVID-19 pandemic. Another study in Iran found a 13.8% increase in hospital admissions due to alcohol intoxication in the first six months of the pandemic⁷. In addition to the global trend of increasing alcohol intake and the effect of the COVID-19 pandemic on this trend, Iranians believed that drinking ethanol can prevent or treat COVID-19³⁴. Similar to the mentioned studies, we found a significant increase in the slope of ethanol intoxication in our center which changed the downward trend of ethanol intoxication before the pandemic to an upward trend.

Consuming and marketing ethanol in every form (e.g., beer, wine, etc.) is illegal in Iran. However, a meta-analysis found a 12% prevalence of last 1-year alcohol consumption in the general population in Iran which was 15% higher in young people³⁵. This prevalence is not consistent in different regions of Iran due to cultural differences. Due to the illegal use of handmade alcoholic beverages in Iran, methanol intoxication is a public health issue. In a report, 768 intoxications were reported in 23 days, of which 69 died. Our study showed that the trend was upward for methanol intoxication before the pandemic. The COVID-19 emergence increased methanol intoxication in our center which can be explained by several reasons including the shortage of ethanol at the beginning of the pandemic as ethanol was mainly used for hand sanitizers in addition to the myth that ethanol can prevent and treat COVID-19 which increased the use of handmade beverages in Iran resulting in more methanol intoxication.

The Centers for Disease Control and Prevention (CDC) reported that about 50% of deaths due to drug overdose in the United States involved synthetic opioids³⁶. This study found that the trend is upward with an increase of 1040% in opioid-related mortality from 2013 to 2019. Another study conducted by Olfson et al. found an increase in the rate of opioid overdose deaths from 2000 to 2017 in the United States; however, the proportion of opioid-related suicide reduced from 9 to 4%³⁷. Although there are several challenges in collecting accurate data for opioid overdose in Iran³⁸, a study estimated that about 65% of drug-related deaths in Iran are due to opioid overdose³⁹. Similar to the global trend, we found an upward trend for opioid overdose in our center. Interestingly, the pandemic dramatically increased the slope of opioid overdose. This finding is in line with a study conducted in the United States which showed that COVID-19 significantly increased the rate of opioid-related deaths⁸.

Regarding total drug poisonings, rising trends were observed both before and during the pandemic. Drugs investigated comprised benzodiazepines, anti-depressants, anti-psychotics, and analgesics. The change in poisoning trends from these drugs might reflect the effect of the pandemic on the mental status of populations, attributable to social distancing and isolation, economic problems, and uncertainty about the future of the pandemic^40–42. Several early studies reported conflicting results for benzodiazepine use after the initiation of the COVID-19 pandemic, with some reporting an increase in their use^43,44, and some reporting a decrease^45,46. A more recent study conducted in Spain which compared the patterns of benzodiazepine use and misuse in the first two years of the pandemic and compared it with the previous 2 years found that benzodiazepines used were significantly higher during the COVID-19 time, in particular clonazepam, the most frequent benzodiazepine consumed⁴⁷. In anti-depressant use, an ITS study conducted in Israel, the use of anti-depressants changed from a decreasing trend to an increasing trend during the pandemic⁴⁸. This was observed in nationwide data from Europe and the United States as well^49,50. This further emphasizes the substantial risk that the pandemic posed to people’s mental health to the extent that it is described as a “mass social trauma”⁵¹. All these increased uses of drugs increase the chance of abuse and poisoning from them.

Stimulant poisoning had an increasing trend before the pandemic, however, there was a sudden decrease at the beginning of the pandemic. Stimulants consisted of amphetamines and cocaine. In a study conducted on young children, no immediate change was observed in cocaine and amphetamine ingestion rates at the pandemic initiation time¹⁰. However, a decreasing trend was observed for amphetamine ingestion after the pandemic. Similar to our study’s findings, in an interesting study that assessed the use, price, and availability of several drugs and substances worldwide, a decrease in amphetamine and cocaine use was observed during the pandemic⁵².

As the most widely used illicit substance worldwide, cannabis was estimated to have 192 million users in 2018⁵³. Although opium has long been the main illicit drug used in Iran, in recent years, cannabis has also increased use mostly among high school and university students^53,54. This increasing trend was also reflected in poisoning patterns found in our study. However, the pandemic led to a sudden decrease in the poisoning related to cannabis and also the trend. This is in line with findings from a community survey in the United States⁵⁵. Conversely, in the global estimates, 42% of countries reported increased use of cannabis⁵². It should be noted that there might be increased use of marijuana during the pandemic due to the mental effects of the pandemic, however, the poisoning which stems from the dangerous use of cannabis might have decreased.

Finally, there is not much reported data regarding poisoning from pesticides in the literature. However, an increasing trend after the pandemic has several implications for policymaking. Intentional and unintentional uses should be addressed as the pesticide’s use has increased in recent years⁵⁶.

Our study has several policy implications which should be highlighted. First, is the fact that there was a sudden decrease in the rate of poisoning while the trend was increasing for most of the substances. Policymakers should take this into consideration in similar situations such as pandemics or even endemics. The increase in methanol and ethanol intoxication is of high importance since it can be a potentially lethal condition with similar events in the past in the country. Educating the normal population and preparing for this rise among healthcare systems in these conditions could be doable actions for future crises. Future studies should focus on the impact of other aspects of the COVID-19 pandemic such as vaccination and each wave of the COVID-19 pandemic.

Despite investigating a large number of patients for assessment of trends in a referral center of poisoning in Iran, this study has some limitations. First, due to the single-center nature of our study, the generalizability of our findings might be threatened. Second, there are some inherent biases for ITS analysis, including history bias, cofounders, and the impact of other interventions and policies during the assessed period^57,58. Third, although one of our findings might be a sudden reduction in poisoning-related hospitalizations, the fear of referring to hospitals and social distancing might have been effective. Finally, several factors such as the introduction of vaccines, different waves of COVID-19, and lockdown policies might be other determinants of drug/substance abuse that might not be interpretable with a single stratification into pre-COVID and COVID time. All of these suggest further research on these trends considering these factors and comparing the effect of each on overall poisonings.