In this study, we explored the development of SIP episodes during the COVID-19 pandemic. Although the number of individuals with SIP decreased during the COVID-19 years, there was an increase in the number of episodes. There was a significant decline in cannabis-induced psychosis, but a rise in SIP episodes caused by amphetamine and multiple substances. Most people experienced more than one episode of SIP, but among those with several SIP episodes, most had several episodes triggered by the same drug. However, there was an increased likelihood of being diagnosed with different types of SIP during the two pandemic years 2020 and 2021 than in 2019. This involved more people changing from amphetamine-induced psychosis to psychosis induced by multiple substances and vice versa, but in fact fewer from cannabis-induced psychosis to psychosis induced by other drugs and vice versa, apart from the year 2021.

The pandemic with its restrictions exacerbated the health conditions of people already marginalized in society [32]. Thus, another explanation for the high number of SIP episodes during the pandemic years might be that those with SIP were already in a low socioeconomic position, with few alternative ways of adapting to restrictions, and a higher consumption of drugs, which may have led to more SIP episodes.

Interestingly, despite an overall decrease in the number of individuals experiencing SIP during the COVID-19 years, we observed an increase in the frequency of SIP episodes during the same period. Fewer individuals with more episodes could be viewed as a polarization of use, which has also been seen in alcohol use during the pandemic, where those with previous high consumption increased their use, while those with previous low or moderate consumption drank less alcohol [33].

Although many individuals with multiple SIP episodes had most of these episodes triggered by the same substance, there was a higher likelihood of individuals being diagnosed with different types of SIP during the pandemic than in the prepandemic year of 2019. People in Norway with concurrent MHD/SUD reported needing stronger drugs to cope with the pandemic, thus not showing fidelity to their usual drug or dosage [17]. Likewise, in a study from the UK, people who injected drugs reported changes in drug use patterns and transitions, especially to cocaine, benzodiazepine and pregabalin, during the pandemic [34]. These transitions to different drugs might reflect the occurrence of SIP and transition from one type of SIP to another, as our study revealed. Our data showed a decrease in SIP due to cannabis and an increase in SIP involving amphetamine and multiple substances in 2020, and this pattern was also observed in the changers, although the highest transition rate was to SIP involving multiple substances. Another reason for this development could be the changes in the drug market due to different types of restrictions. We also know that during the pandemic the illicit market was shifting toward more new psychoactive substances [35], the most prevalent of which were synthetic opioids, synthetic cannabinoids, and synthetic cathinones.

Our results may also reflect changes in general substance availability. Although the drug markets quickly rebounded after the onset of the pandemic, certain trafficking dynamics were strengthened during COVID-19, including larger shipment sizes, increased use of private aircraft, expanded use of waterway routes, and contactless drug transactions [36]. The reduced availability at the beginning of the COVID-19 pandemic and the associated higher price of certain drugs might also explain the significant decline in cannabis-induced psychosis and the concurrent rise in SIP episodes caused by amphetamine. Cannabis tends to have sedative effects, which may not have been desirable during periods of high stress or uncertainty. People may have sought the stimulating effects of amphetamines to combat the lethargy, low motivation, or depression associated with prolonged lockdowns and isolation [37].

Amphetamine-type stimulants are widely used as street drugs due to their affordability but have a high potential for addiction. Data from the Netherlands indicate that the number of methamphetamine laboratories increased from 9 in 2019 to 32 in 2020 [38]. The consumption of amphetamine in Europe has been rising since 2020 [39] and it has become more potent in recent years [40]. The narcotics report of the Norwegian police [41] reveals an extraordinarily high confiscation of amphetamines in 2020, which indicated a high circulation of this substance. The rise in production, potency and consumption could explain the rise of amphetamine-induced psychosis seen in our data.

The United Nations World Drug Report 2021 describes an increase in the use of cannabis globally during the pandemic [36]. European research also suggests an increase in cannabis consumption during the early months of COVID-19 [42]. However, Norwegian pandemic restrictions included closed borders at the beginning of the pandemic, which led to less smuggling of drugs and a cannabis drought, according to the narcotics report of the Norwegian police [41]. According to the Norwegian Organization for Humane Drug Policies, the price of cannabis in Norway rose 500 percent from 2019 to 2020 [43].

Our study shows that most SIP episodes were recorded as psychosis induced by multiple substances (F19.5), both before and during the COVID-19 period. This is consistent with previous research [5, 44-46], which found that individuals experiencing SIP were more likely to be involved in the abuse of multiple substances [47]. Also for substance users without a SIP diagnosis, polysubstance users are more likely to experience psychotic symptoms than those who predominantly use amphetamine or cannabis and alcohol [48]. Furthermore, many people diagnosed with F19.5 have probably used a mix of stimulants and a substance to end the binge or counter the effect of the stimulants, such as alcohol, benzodiazepines, or cannabis.