It is worth noting that the set of sociodemographic characteristics of the sample studied here appear to be associated with an increased risk for presenting mental disorders, since the average included subjects were young, male adults, who were single and unemployed. These characteristics have been associated with this increased risk in studies previously carried out and similar to ours (24, 25).
It is important to highlight the high percentage of unemployment that the participants had, some authors have observed an increase of 1.5 to 2 times more the risk of being hospitalized in unemployed or economically inactive subjects (26).
It is documented that people with severe mental illness, such as schizophrenia and bipolar disorder, have high unemployment rates, with more difficulties in finding and keeping a job, which may be due to low levels of education, stigma, and chronic or recurrence of symptoms (27). The more severe the mental disorder, the greater the association with unemployment or economic inactivity has been reported, as is the case of psychotic disorders (the most prevalent syndrome in the sample studied here), which are associated with less remunerated jobs and integrate the lowest socio-economic strata of a community (26).
In individuals with sociodemographic characteristics such as those observed here, there is usually an increase in the rate of psychiatric hospital readmissions. Bui and Wijesekera (2019) found a statistically significant association between the unemployment rate of the population and the rate of hospital admissions, this association was closer in case of also having a substance abuse disorder (28).
According to a recent study carried in South Africa on people with mental illness who were hospitalized, unemployment is often more common in patients with a psychotic disorder. This may be due to the deterioration that accompanies severe and persistent mental disorders, such as schizophrenia, and that leads to conditions of inequality that prevent them from carrying out the fair competition in the labor market (29). A study carried out in Colombia with people who had been admitted to a psychiatric hospital reported similar results to those found in our study; the sample was made up of single young men, of low socioeconomic strata, in them, 62.6% had ages between 18 and 34 years, with low levels of education, 49.5% presenting the diagnosis of schizophrenia or other disorders psychotic. They also reported high percentages of unemployment, however, they observed that this phenomenon was higher (51.6%) among those with a dual diagnosis compared to those without substance abuse (45.5%) (30). Specifically, there is consistent evidence of the relationship between the association of unemployment with substance abuse in young adults (25, 31, 32,). Besides, almost a third of patients with chronic psychotic disorders meet the criteria for dual illness, with a three-fold higher prevalence in men, in whom a lower age at their first hospitalization and a greater number of hospitalizations compared to people with similar characteristics, but without a history of consumption (33).
All this accounts for the implicit relationship between the variables unemployment, substance use, and severe and persistent mental disorder. This combination generates in the people who present it, an entity that has a different clinical impact and carries a higher risk of admission at younger ages, a greater number of readmissions, a reduction in quality of life, and greater dysfunction (34, 35).
On the other hand, there is a striking increase in the incidence of the diagnosis of "psychotic disorder induced by substance abuse" as the main admission diagnosis, since in previous studies in our environment this nosologic entity was not considered as one of the first 3 causes of admission. This reflects a negative repercussions that are beginning to appear in the social fabric of the region due to the influence of the overwhelming drug trafficking and consumption, thus reflecting the newer problems that our society is experiencing (36, 37).
According to the data obtained, the most commonly abused substances in the studied sample in the last 3 months were: tobacco (46.6%), ethanol (45.9%), cannabis (34.3%) and methamphetamines (32.8%), similar to reports in the study carried out by Rodriguez and Colls in Spain, where tobacco, ethanol, and cannabis were the substances with the highest use before hospitalization for mental illness, differing only by the fourth substance in frequency, where cocaine replaced Methamphetamines (38).
Regarding tobacco (the most used substance by the patients in this study), its relevance lies in the fact that it exerts a negative effect among the patients under treatment with antipsychotics, since the components of the tobacco are known to be potent inducers of the enzymatic cytochrome P450 complex, in particular, the 1A2 isoform, increasing the rate of biotransformation of drugs that are metabolized by this enzyme. This increased metabolism of some antipsychotics (such as olanzapine and clozapine) results in a reduction in their plasma concentration, which may complicate the evolution of their pathology, even leading to the current relapse responsible for their latest hospitalization (39).
Regarding ethanol, it is known that its abuse precedes the consumption of other substances, finding ethanol in the category of "entry drug" (40). Previous studies show the existence of a clearly defined sequence of drug abuse that begins with licit substances and leads to illicit drugs, with ethanol being the most common entry substance. It is worth considering then that future interventions should be directed at alcohol abuse prevention, management, and rehabilitation (41–47).
Cannabis use (34.3%) was in third place among the most commonly abused substances in the last 3 months and first place among illegal substances. It also ranked second (14.9%) in terms of severity of use, second only to methamphetamine (16%). That is, cannabis and methamphetamines not only have a high prevalence in terms of their abuse, but they were the 2 substances that were used most dangerously, according to the ASSIST scores. Regarding the use of cannabis and its association with psychosis, it has been observed that patients with psychotic disorders have a higher prevalence of cannabis use and consumption disorder compared to the general population. Besides, compared to those who do not consume this substance, cannabis abuse increases the risk of developing Psychosis, severe and continuous consumption increases the risk of developing schizophrenia. There is also a dose-dependent association, with an increased risk of psychosis in frequent users (48). Consumption is also associated with earlier onset of psychotic disorders, occurring on average 2.7 years earlier than in people who do not consume it (48). Cannabis users with psychotic disorders are at increased risk of relapse, hospitalizations, poorer adherence to treatment, and greater severity of positive symptoms. Discontinuing use reduces the risk of progressing to a poor prognosis (48).
Just as there is a “sociodemographic phenotype” for the entire sample, the specific sociodemographic characteristics of methamphetamine users are also relevant. They are the youngest group of people compared to the rest of the sample, with the shortest disease evolution, the fewest number of hospitalizations, a higher GAF score at discharge. Except for hallucinogens and opioids abuse, methamphetamine abuse was associated with the greatest severity in consumption (according to the ASSIST scores). They are a group with great potential for a timely intervention prior to their evolution towards a “revolving door” phenomenon that is difficult to manage. Given that, in their last hospitalization, their stay did not last for more days compared to the rest of the sample, did not have a greater number of prescribed psychotropic drugs, they entered with similar severity, but were discharged with greater recovery. This evidenced by the GAF score at both times (49, 50). It would then be necessary to devise public policies or a specific management plan to avoid relapses in these patients upon discharge (51).
In Mexico, Medina-Mora et al. reported that the consumption of methamphetamine ranks third of those substances for which treatment is sought (14.3%), however, in regions near the border, it occupies the first place of attention (31.2%) (37). In the present study, the consumption of methamphetamines ranked fourth, with 32.8%, among the most used substances in the last 3 months. Of the patients who consume, the majority (48.9%) report severe consumption. According to reports from the Inter-American Drug Abuse Control Commission in 2019, Mexico ranks second in prevalence, in the general population, of methamphetamine use with 0.9%, being higher in men (52). However, the source of monitoring is based on population-based surveys, which have limitations that reduce their usefulness for evaluating short-term changes, decrease the possibility of obtaining representative figures for specific vulnerable groups, and have limitations regarding the validity of the information derived from the social stigma surrounding consumption, so these figures may be underestimated (53).
The risks in the consumption of this substance directly impact the public health of the country to a greater degree than the consumption of other substances, its use usually increases by 3 or 3 fold the risk of presenting psychotic symptoms, particularly if it is used in large quantities or an early age onset (54.55). Methamphetamines cause an overflow of dopamine in the striatum, leading to excessive glutamate release in the cortex. Excess glutamate can, over time, damage cortical interneurons. This damage causes dysregulation of the thalamocortical signal, which can result in the presentation of psychotic symptoms (55).
Regarding predictive analysis, the logistic models for methamphetamines, ethanol, and cannabis had a high power to explain the totality of the consumption phenomenon (86.92%, 73.72%, and 85.75% respectively). In other words, each of the variables that made up the models, by being present together with the other variables, can predict with significant statistical power the possibility that in a similar scenario there may or may not be a risk of consuming any of these substances.
It is interesting to observe how the findings in our study and others suggest that the risk of illicit substance consumption considered as "more dangerous" is increased if other substances for legal consumption were previously used, or if 2, 3 or more substances were added before the arrival of cocaine or methamphetamine use. It is of utmost importance to highlight that the sociodemographic variable with the highest weight in these models was the years of study, with an effect size of -1.73, which shows that at a lower school level there is a greater risk of cannabis use, with the consequent risk that this entails for being one of the "entry drugs" for the consumption of other illicit drugs. It is also relevant to emphasize that at a younger age the risk of consumption of other substances increases, with a particularly large effect size (from − 0.63) being observed for the use of methamphetamines, in the presence of consumption of other substances (alcohol, cannabis or cocaine).
As part of the limitations of the study, we found a high percentage of people who did not undergo the toxicological test in the first 24 hours of admission (23.1% did not have this test, mainly due to the level of agitation reported by nursing), which reduced the detection figures for acute substance use. Besides, the fact that the methamphetamine detection test has a reduced positive predictive value in terms of its completion time concerning the date of last use (detects a positive use only if it was performed within 48 to 72 hours ) further reduced the percentage of people identified as consumers of this substance in the last 12 weeks (56).
However, we consider that the most important limitation of our work is the predictive level that the results show us, since being an exploratory and observational study, the evidence presented here only allows to establish possible associations and suggestions for future studies to be carried out to determine if the sociodemographic and clinical characteristics mentioned here as “risk variables” could be replicated in prospective studies designed to obtain a better quality of evidence.