The main objectives of this study included the assessment of the evolution of the prevalence of cannabis use among first-year university students in Spain. According to our results, cannabis use ever in a lifetime showed an upward trend from 2017 to 2019, which otherwise was not reflected in an increase in past 30 day use, possibly indicating a higher number of students who decided to try cannabis but did not continue using it, in line with recent national trends [16].

The evolution of the prevalence of cannabis use from 2012 to 2019 showed values between 28–34% of students in the past 12 months, which are higher values than the national average for 15–24 years old, whose value was 22.1%. In the past 30 days, the prevalence rates were between 16–19%, which is like the national average of 15.9% [16]. Nevertheless, it was observed that our results on the prevalence of use were much higher than the European average (19.2% in the past 12 months, 10.3% in the past 30 days) for people aged 15–24 years [11], coinciding with other authors that Spain is one of the countries with the highest cannabis use in Europe [13].

About another objective of the study on the assessment of the potential impact of the COVID-19 pandemic, our results showed that during the lockdown period the prevalence of cannabis use decreased considerably, especially in the frequencies of the past 12 months (32.1% in 2019 to 26.9% in LD) and the past 30 days (16.2% in 2019 to 11.8% in LD). In the new normal period, these prevalence rates increased again. These results are consistent with other authors’ findings of lower cannabis use during COVID-19 restrictive periods in university students [38,39] and the general population [40,41]. This could be explained by the large number of social restrictions that influenced the reduction of mainly, occasional use, as other authors have suggested [38,39] as well as a possible lower availability [42,43] of the substance because of the mobility restrictions, especially during the first lockdown [11,23]. Likewise, in alcohol use, a decrease was observed during the lockdown in the past 30 days prevalence, with a reduction from 78.6% in the before COVID-19 period to 63.8% during the lockdown, recovering in the new normal period (77.7%) with no differences between sexes [44].

Disaggregating data by sex, it was observed that males reflected higher prevalence rates than females, although in the later years of the study these differences were not statistically significant. Although men have historically shown higher prevalence rates of cannabis use, in recent years it has been observed that women are increasing their prevalence rates, narrowing the cannabis use gap between men and women [45,46,47]. The analysis of the evolution in the next few years is a key point to shed light on this trend in university students.

On changes in patterns of use during the pandemic, it was found that among students who used cannabis, 47.2% increased their use since the beginning of the pandemic and 32.5% did not change their use. This represents a large percentage of students who increased or did not change their use (79.7%) compared to only 20.3% who decreased it. These results may be consistent with other authors’ findings of a reduction in occasional use but an increase or maintenance of use in many regular users in this period [48,49,50,51,52]. These patterns of use distribution may be related to an increase in dependence on the substance among regular users, so that despite social restrictions they continued using cannabis solitarily, which is common among regular users [27,53].

In line with this, it is worth noting our results on cannabis use as a coping strategy, as solitary cannabis use has been related to coping motives [53]. It was observed that among users who reported increasing their use, more than half reported using to cope with the pandemic, compared to 23.3% who reported decreasing their use. These data are of great interest since coping has been associated with an increase in depressive symptoms, increased risk of dependence, social vulnerability, and withdrawal symptoms [19,54,55,56], among other problems. Therefore, educating and managing coping strategies with students is of great interest to prevent problematic use and CUD among the university population.

Regarding places of use, parties were found to be among the most frequent places of use, reflecting the large number of students who consume in the social context. Use in the usual home was much higher among students living with roommates than among those living with their parents, which is consistent with other studies [18,57]. However, during the LD period, both students, living with roommates and living with their parents, increased their use. This contrasts with the reduction in cannabis use during LD that was observed in the evolution graphs reflecting a preference for consumption in the usual residence during the restrictive social measures. Moreover, this increase in use at home could reflect a high dependence on use coupled with a permissiveness of cannabis use in the home environment [58] or hiding it. The age of onset was similar across the time series, with no significant differences between the sexes. It was 16.6 years, which is lower than the national average (18.5) [16], but it must be considered that at the national level this data is calculated with a population aged 15–64 years.

The results obtained in this study should be interpreted with caution, as this study has some limitations. Firstly, the limitations of a cross-sectional study design make it difficult to provide causality, but as our main objective was to study the prevalence, we believe that the design is suitable for this purpose. Next, due to the uniHcos questionnaire aims to collect data on different lifestyle habits, variables about cannabis amount consumed or the form of cannabis use have not been collected. However, it has been established that among Spanish people, the most common form of use is marijuana as a joint [16]. In addition to this, data collection was obtained by a self-administered questionnaire not standardized, which could over- or underestimate the information obtained, especially considering the biases in terms of providing information on substance use and cannot be well generalized to other university populations or the entire population, although it could be considered a first step to understand trends that should be deepened in future research. Finally, there are also limitations in terms of the sample, as there was a higher percentage of women than men, which is expected to be controlled by stratification by sex, as well as differences in sample size in some periods.

On the other hand, it is interesting to highlight some of the strengths of our study, such as the possibility of understanding cannabis use in the Spanish university context after an analysis of its evolution over time and considering the influence of the pandemic, which provides new lines of research and new preventive strategies for this vulnerable population.