The main findings of our study are as follows: Compared to the control group of 30-year-olds, prothrombin time (PT) was lower in the Multiple-Substance and Methamphetamine groups. Additionally, activated partial thromboplastin time (APTT) values were higher in the Cannabinoid group. Among the substances studied, aspartate aminotransferase (AST) levels and alanine aminotransferase (ALT) levels were lower in both the Methamphetamine and Opiate groups. Furthermore, AST levels in the Alcohol group were elevated compared to the healthy control group aged 45. We also observed significant differences in AST, ALT, PT, APTT, and platelet (PLT) values based on the type of substance used by individuals.

Our findings indicate that PT values were lower in both the Multiple-Substance and Methamphetamine groups when compared to the 30-year-old control group. This shortening of PT may predispose individuals to serious health issues, such as thrombosis, myocardial infarction, stroke, or deep vein thrombosis [23]. Research has indicated that methamphetamine users face an increased risk of thrombosis, resulting in a higher likelihood of cardiovascular complications such as acute myocardial infarction [24,25]. A study by Sharma et al. also found that cocaine use, a stimulant like methamphetamine, contributes to a prothrombotic condition [26]. These findings align with our study, highlighting the need for caution regarding thrombotic conditions and associated cardiovascular complications in these patients. In the Multiple Substance group, the short prothrombin (PT) duration observed can be interpreted as consistent with the aforementioned literature, given the use of methamphetamine among these individuals. Furthermore, the presence of cannabinoid use in the Multiple Substance group adds complexity to the analysis. Therefore, further research examining the specific amounts of methamphetamine and cannabinoid use in these patients would be beneficial.

In the context of APTT values, the findings indicate that the APTT values in the cannabinoid group were significantly higher than those observed in the control group. A study conducted by Levendal and Frost demonstrated that the administration of a plant-based cannabinoid extract to Wistar rats resulted in an increased clotting time [27]. In addition, contemporary research has established a connection between cannabis use and conditions such as hemoptysis and alveolar hemorrhages, which appear to be consequences of its anticoagulant effects [28,29]. Conversely, it is important to note that there are discordant studies that suggest cannabinoid use may exert procoagulant effects, ultimately leading to thrombosis [30,31]. When analyzing the current data in conjunction with the existing literature, it is evident that cannabinoids may contribute to APTT prolongation associated with anticoagulant properties. Consequently, it is advisable to assess patients utilizing cannabinoids with respect to their bleeding risk. Given the contradictory evidence surrounding the relationship between cannabinoids and coagulation, further targeted and advanced investigations are warranted.

In addition, research examining the effects of opiate use on coagulation factors has revealed no significant association between opiate use and levels of prothrombin time PT, APTT, or INR, a finding that aligns with our results [32,33].

Regarding PLT (platelet) values, the alcohol group exhibited lower values compared to the multiple-substance group and the methamphetamine group, while no significant difference was observed when compared to the control group. Research indicates that alcohol consumption can lead to a decrease in platelet count and aggregation, but there are also studies suggesting that acute alcohol intake may increase platelet activation [34,35]. Although these findings seem contradictory in light of our data, it is evident that alcohol influences platelet function, and further research in this area would be advantageous.

In terms of AST values, the alcohol group had higher readings than the opiate group, methamphetamine group, cannabinoid group, multiple-substance group, and control groups. Moreover, AST values in the methamphetamine and opiate groups were lower compared to those in the 30-year-old control group. For ALT values, the alcohol group showed higher levels compared to the methamphetamine, multiple-substance, and opiate groups; however, there was no significant difference between the alcohol group and the control group. A study by Harris and colleagues indicated that liver function test values tend to increase after alcohol consumption [36]. Consistent with our findings, many studies have established that AST is more closely associated with alcohol consumption than ALT [37]. A high AST/ALT ratio is known to indicate advanced alcoholic liver disease [38]. Studies have demonstrated that methamphetamine use can lead to liver damage through mechanisms such as oxidative stress, inflammation, and disruption of the cell cycle [39,40]. An experimental study by Atici et al. also found that morphine addiction elevated liver function test values [41]. In contrast, a case–control study by Bazmi et al. found that liver dysfunction was less common in the group using opioids [42]. When integrating these findings from the literature with our results, it can be concluded that alcohol consumption, in particular, contributes to liver damage. The presence of conflicting data in the literature regarding the effects of methamphetamine and opiate use on the liver, together with our findings, can be explained by the fact that liver enzyme levels are influenced by factors such as the duration of substance use, nutritional status, and muscle mass [42]. Careful monitoring of liver function in these patients would also be beneficial.

A significant association was found between smoking status and diagnostic groups, as all individuals with substance use disorders were regular smokers, while approximately half of the control participants reported smoking. Despite this high prevalence, no significant differences were observed between smokers and non-smokers in liver enzyme or coagulation parameters (p > 0.05 for all). This finding aligns with prior research showing that smoking is highly prevalent among individuals with substance use and psychiatric disorders [43], yet its direct biochemical effects are generally modest.

Although nicotine exposure has been implicated in influencing hepatic metabolism and hemostatic regulation through mechanisms involving oxidative stress, endothelial activation, and changes in platelet aggregation [44,45,46], human evidence suggests these effects are generally mild and not clinically significant in otherwise healthy individuals. Recent data indicate that cigarette smokers may show minor elevations in certain liver or coagulation markers, but findings remain inconsistent and of limited physiological relevance [45]. Accordingly, the absence of significant differences in ALT, AST, PT, aPTT, INR, and PLT between smokers and non-smokers in our study supports the interpretation that nicotine-related systemic effects are modest. Therefore, the biochemical alterations observed among the diagnostic groups are more likely attributable to substance use rather than to smoking itself.

In our study, the average age in the Alcohol group was found to be higher compared to other groups using substances. No significant age differences were observed among groups using drugs. In a study by Stevens and colleagues on this subject, similar to our findings, it was shown that trying various substances other than alcohol is more common among young people, while alcohol is preferred over other substances among older people [47]. In our study, more appropriate comparisons were made by selecting a control group with similar characteristics to the Alcohol group and a control group with similar characteristics to the substance groups’ average age.

This study has several limitations. Its retrospective and non-randomized design limits the ability to establish causal inferences. The quantity and duration of substance use were not precisely quantified, and the degree of nicotine dependence or the number of cigarettes smoked per day was not assessed, which may have influenced some biochemical parameters. In addition, for illicit substances such as methamphetamine, cannabinoids, and opiates, reliable quantitative dose information is rarely available in routine clinical records, which is a common methodological limitation in substance use research [48,49,50]. Because detailed information on cumulative dose and exact time since last substance use was not available for all patients, early withdrawal-related physiological and biochemical alterations may have influenced the measured liver and coagulation parameters, even though all biochemical assessments were performed on the first day of admission to the detoxification unit, and this should be considered when interpreting our findings [51,52]. Additionally, the exact proportions of methamphetamine and cannabinoid use within the multiple-substance group remain uncertain, and laboratory parameters were evaluated only at admission without follow-up measurements. Finally, because this was a single-center, retrospective study, the generalizability of our findings may be limited. In collaboration with other relevant centers in the future, prospective multicenter studies are needed to increase the generalizability and to confirm our results.

However, the study also has notable strengths. It was conducted in a specialized clinic with well-organized patient records, involved a relatively large and well-characterized clinical sample, and included two age-matched control groups, allowing robust comparisons across diagnostic categories. Furthermore, it is one of the few studies to examine liver and coagulation parameters simultaneously across multiple substance-use groups while also accounting for smoking status. These features, together with the standardized biochemical assessments at baseline, enhance the reliability, interpretability, and clinical relevance of the findings.

Despite several limitations, our study provides a unique contribution to the literature by demonstrating substance-specific alterations in both liver and coagulation parameters within the same clinical population. Notably, the identification of significantly lower PT values in methamphetamine and multiple-substance users and prolonged aPTT in cannabinoid users highlights differential haemostatic risks associated with specific substances. Additionally, the finding that smoking status did not significantly affect biochemical outcomes strengthens the interpretation that the observed alterations were primarily substance-related rather than nicotine-induced.

In order to clarify these relationships and determine the specific mechanisms underlying substance-related liver and hemostatic changes, future studies with prospective, randomized controlled, and biomarker-based designs that also consider the amount and duration of substance use and other possible factors are necessary.