The results of the present study show that there are no significant differences in the levels of depression among the subjects according to the substance consumed. Subjects with a more severe diagnosis of depression were the consumers of benzodiazepines, followed by consumers of alcohol, heroin, cocaine and cannabis, in different percentages. According to the literature found on the one hand, high depressive symptomatology without the diagnosis of depression is observed in alcohol and cannabis users, although on the other hand, there are many subjects diagnosed with depression, not only with the symptomatology, in the case of alcohol [17,18,19].

According to research by Rojo-Mota et al. [11], no significant differences were observed in the levels of cognitive deterioration among the subjects depending on the substance consumed. However, here, a significant difference was found between cannabis and alcohol consumers, which would indicate that people who consume alcohol obtain a lower score in the MoCA inventory, showing greater cognitive deterioration than people who use cannabis, or similarly, that cannabis users have less cognitive impairment than alcohol users. However, it is necessary to highlight that these results obtained indicate that cognitive impairment was detected in 78.7% of participants compared to non-cognitive impairment in 21.3% of the sample analyzed. It should also be noted that cocaine users have the worst level of cognitive impairment and cannabis users have the best cognitive functioning, similar to results reported by Rojo-Mota et al. [11] and Bruijnen et al. [8].

Regarding the sociodemographic variables, a statistically significant relationship was found between cognitive deterioration and the variables of the subject’s age and the time of consumption. This would indicate that a lower score obtained in the MoCA inventory, which shows a greater cognitive deterioration, is linked to a greater current age and time of consumption found in the subjects. Therefore, consumers of toxic substances that have greater cognitive deterioration are older and have spent more time consuming. Contrary to other studies [11], where no statistically significant relationships were found between the cognitive deterioration of consumers and the time of consumption, in the present study, a statistically significant relationship was also found between the sociodemographic variable of the subject’s current age, time of consumption and age of onset. This indicates that people with a more advanced age have been consuming psychoactive substances for longer and began to consume at later ages. Likewise, a statistically significant relationship was observed between the time of consumption and the age of onset, which would mean that consumers who have been spending less time consuming these types of substances began to consume them at a later age.

In the statistically significant results found concerning the relationship between cognitive deterioration and the different sociodemographic variables depending on the substance consumed, it was found that the heroin, alcohol and benzodiazepine users who obtained a lower score in the MoCA inventory, which would mean greater cognitive deterioration, were older. This emphasizes that consumers of benzodiazepines with a lower score in the MoCA inventory, that is, with greater cognitive deterioration, began their consumption at a later age. Finally, with regard to the cocaine and cannabis users, no statistically significant relationships were found between cognitive deterioration and the current age of the subjects. A statistically significant relationship was also found in the consumers of alcohol, cocaine and benzodiazepines between the variables of current age and age of onset of consumption. These results showed that the consumers of these three substances with greater age began the consumption of these at a later age.

With regard to the variable consumption time, three statistically significant relationships were found with the MoCA inventory variables, current age and age of onset of consumption depending on the substance consumed. Firstly, regarding the cognitive impairment and time of consumption variables, the findings demonstrated that, in heroin and alcohol users, subjects who had higher scores in the MoCA inventory, with less cognitive decline, had been consuming for less time. Secondly, the variables of consumption time and current age showed a statistically significant relationship in the users of heroin, alcohol, cocaine and cannabis. As such, consumers that have consumed for a greater period of time are older. Thirdly, with regard to the variables of time of consumption and age of onset, statistically significant relationships were found in the consumers of heroin, alcohol, cocaine, cannabis and benzodiazepines.

As for the substances analyzed, for alcohol consumers, the age of onset of consumption was at 16.65 years, which is comparable with the results of other studies that reported an age of 16.8 years. It was also found that the duration of consumption was 29.52 years, which was greater than the 14.9 reported in other studies [32].

Finally, in relation to the relationship between cognitive impairment and depression in consumers of these types of substances, as in other recent studies [33], a series of statistically significant relationships were found. On the one hand, it was observed that consumers who did not have depression scored lower in the MoCA inventory than people who had moderate depression. This shows that consumers without a diagnosis of depression have greater cognitive deterioration than those who have moderate depression. Or, similarly, subjects with moderate depression have lower cognitive impairment than those who do not have a diagnosis of depression. On the other hand, consumers with moderate depression scored higher in the MoCA inventory, that is, they had lower cognitive deterioration than people with severe depression. This, in turn, means that consumers with severe depression have greater cognitive decline than those diagnosed with moderate depression.

One of the limitations of this study is its exploratory design. It was intended to analyze the relationship between the type of consumption with depression and existing cognitive impairment. Although the age of onset of use and years of substance use were included in the present investigation, other studies have also assessed the residual harm of drug use [34,35,36]. Future research could use a longitudinal design to assess the impact of sustained use over the years on depression and cognitive impairment. In addition, a longitudinal design could shed light on the directionality and causality of the relationships studied. Another limitation comes from the classification of the sample according to the main substance of use; however, most drug users are polydrug users or have been combining the type of substance over the years. In future studies, it would be interesting to analyze whether different combinations of drug use lead to different symptoms of depression or cognitive impairment.