■ Introduction

Opioids are substances that bind to opioid re­ceptors in humans. Many have psychoactive, analgesic, and antitussive effects and are therefore used both medically and recreationally. In medicine, they are an essential ingredient in many pain­- killers used to treat post-operative, cancer and
chro­nic pain [1]. The most common opioids used for pain-relief include codeine, tramadol, oxycodone, morphine and fentanyl. They are administer­ed to patients in various forms: immediate-acting or extended-release tablets, intravenously or in transdermal patch form. Currently, a large part of the recreational opioid market consists of opioid analgesics [2].

When used recreationally, opioids rank among some of the most dangerous psychoactive substances due to their high addictive potential and risk of fatal overdose [1]. Intravenous injection is well-known dangerous behaviour associated with opioid use. People who reuse the same needles and syringes are particularly vulnerable to complications, most commonly viral and bacterial infections.

According to the World Health Organization (WHO), substance dependence is the most stigmatised social phenomenon – more so than homelessness, human immunodeficiency virus (HIV) infection or alcohol use disorder [3]. Addicted people are judged to be at fault for their situation and are considered more dangerous and threatening than people with other diseases or mental health disorders [4, 5]. The consequence of stigmatisation is that it makes recovery from dependence and  seeking help more difficult. Addicted people are “doubly punished” because, in addition to the direct consequences of dependence, they are socially ostracised and condemned [5]. Moreover, people who take opioids for chronic pain management can also be stigmatised [6].

Disgust

Disgust is considered a basic emotion that is present in all cultures [7]. In the context of evolution and cultural development, it has a protective function for both the individual and the community – it protects against contagion, but also against culturally unacceptable phenomena and even thoughts of mortality [8]. Research studies [8-10] identify various types of disgust:

•  sexual disgust, which protects against reproductive risks like a partner engaging in risky sexual behaviour or incest; 

•  moral disgust, which influences the avoidance of people who transgress social norms, reducing the chances of an attack or unpleasant contact;

•  contamination/interpersonal disgust, which helps avoid infection from people or objects that belong to them; this type of disgust is sometimes linked to moral disgust, as together they serve to protect social order and can be shaped by state and religious institutions;

•  core disgust, which refers to avoiding dirt, spoiled food, body secretions, faeces, cockroaches and rats; 

•  animal-reminder disgust, which relates to aspects of human life that are shared with animals like sex and death.

A trait often studied in the context of disgust and its impact on attitudes towards others is disgust sensitivity (DS), or the predisposition to react with disgust to various stimuli. High sensitivity to disgust is associated with a motivation to avoid contamination and to notice potential bacterial hazards even if not actually present [11]. Jones and Fitness [11] describe it within the framework of error management theory; accordingly, people should minimise the likelihood of making the kind of mistake most likely to cause harm and danger. The cost of omission (eating poisonous food deemed healthy) is higher than the cost of a false alarm (not eating healthy food deemed poisonous). Individuals with high sensitivity to disgust may be more likely to make the mistake of a false alarm rather than an omission and exhibit what is known as hyper-sensitivity [11]. 

A study by Clifford and Piston [12] found that people with high disgust sensitivity were more likely to support harsh and exclusionary policies towards people experiencing homelessness, who are often portrayed in the media as dirty, threatening and sick. Pascal et al. [13] summarise the three main characteristics that make repulsive people stand out: 1) transgressing moral norms, 2) being dirty, and 3) transmitting infectious diseases. All three traits contribute to the stereotypical image of an addicted person. According to Harris [14], different methods of substance use elicit disgust to varying degrees. Injection is perceived particularly negatively as it represents a violation of certain bodily boundaries.

A particularly important study by Montgome­ry et al. [15] examined the relationship between disgust sensitivity, injection anxiety and implicit reactions to injecting drug use. The authors used an Implicit Association Test (IAT) that included a variety of images depicting people injecting substances in two contexts: recreationally or medi­cally. Participants rated the images as pleasant or unpleasant and categorised them as either “recreational drug” or “medical drug”. They also completed a survey assessing attitudes toward drug users. The results indicated that disgust sensitivity did not predict implicit attitudes toward injected drug use. Instead, injection anxiety emerged as the only significant predictor of implicit attitudes. However, no relationship was detected between implicit and explicit measures of attitudes, and no significant correlation was observed between injection phobia and explicit attitudes toward drug users. This suggests that injection phobia may influence automatic affective reactions but not explicit attitudes. Montgomery et al. [15] explained this by differences in task requirements: an immediate fear response in the implicit task versus more
controlled processing in the explicit task. Explicit measures of attitudes were significantly correlated with disgust sensitivity but not with injection phobia. Furthermore, the authors measured explicit atti­tudes without differentiating between intravenous and other forms of use, whereas the implicit measures focused exclusively on intravenous drug use. In this context, the two types of measures may produce different results, as questions about a person who uses drugs could elicit different emotional responses compared to images depicting drug use. This highlights a gap in the literature concerning the influence of disgust on explicit attitudes toward drug users via different routes of administration, thereby justifying further investigation. We aimed to examine whether the relative importance of different dimensions of disgust sensitivity varies across routes of administration.

The following hypotheses were posed: 

1)   the level of social distance towards people using morphine will differ depending on the form of use, being highest for individuals dependent to intravenous morphine, intermediate for those dependent to oral morphine and lowest for individuals taking morphine for medicinal purposes; 

2)   the higher the sensitivity to disgust, the greater the social distance towards morphine users. 

Also, we explored how dimensions of disgust sensitivity were associated with social distance towards people who were addicted to opioids via different routes of administration or medical use.

■ Material and methods

To verify the research hypotheses, an experi­mental online study was conducted with 412 par­ticipants recruited via social media who filled in a questionnaire on the Qualtrics platform. The survey language was Polish. Information about the study was distributed in various online communities on Facebook. The invitation to participate in the study included a notice that the study was about psychoactive substances, to warn individuals who might feel uncomfortable with the subject matter before they even opened the questionnaire. To participate in the study, one had to be at least eighteen years of age and declare no current or past dependence to psychoactive substances, excluding nicotine and caffeine. This criterion was included as an additional safeguard as the study aimed to examine attitudes in the ge­neral population rather than clinical populations. 

First, the participants read the informed consent form to take part in the study. The content of the consent form is available in Appendix 1. To take part in the study, participants had to confirm that they were of legal age and that they were not, and had never been, dependent to any psychoactive substance (except nicotine and caffeine). Next, participants completed the reCAPTCHA and answered demographic questions. They were then asked if they had ever used any psychoactive substance, excluding nicotine, alcohol, caffeine and medications prescribed by a doctor. Those who answered “yes” were additionally asked which psychoactive substances they had used. 

Then, the participants were randomly divided into three groups. They were all presented with a vignette about a man named Jan. However, the vignettes varied across the groups. In the first group, Jan was undergoing treatment for morphine dependence which he administered intravenously, in the second, for morphine dependence which he taken orally and in the third, he was not dependent but was taking morphine to reduce pain following spinal surgery. After reading the vignette, participants had to answer a question about the type of substance used by Jan and how it was administered. This was to exclude from the analyses those who did not pay attention to the elements of the story. The exact content of the stories and the attention checks can be found in Appendix 2.

In the next step, the participants completed a modified version of the Bogardus Social Distance Scale: the Social Distance Scale towards People with Mental Illness, which was used in a study by Lauber et al. [16]. The scale was translated into Polish by M.L. Piotrowska, the author of the paper. Although social distance is not synonymous with prejudice, it is an effective way to measure reluctance to interact with members of a particular social group. It stems from factors like fixed personality traits, previous experiences and exposure to hate speech [17]. The scale consists of six items regarding how close the respondent would be willing to interact with Jan (the person described in the story). Responses were presented on a five-point Likert scale, ranging from 1 – “definitely no”, to 5 – “definitely yes”. Accordingly, the higher the score obtained on the scale, the lower the social distance from the person. However, in further analyses, the scale was reversed to facilitate the interpretation of the results, so the higher the score on the social distance scale, the greater the distance. Participants also completed a knowledge test on opioids though the results were not included in the analyses. 

Finally, the participants completed the Polish version of the Questionnaire for the Assessment of Disgust Sensitivity [8]. This is a scale by Petrovski et al. [18], which assesses the severity of sensitivity to disgust, considering a variety of factors mentioned by theories of disgust, such as the oral domain, animal nature and disgust associated with social interactions. The scale contains a total  of 37 items and consists of three subscales: Core Disgust (14 items), Animal-Reminder Disgust  (9 items), and Contamination Disgust (13 items). Each item is rated on a five-point Likert scale (ranging from 1 to 5) with higher scores indicating greater disgust sensitivity. 

One attentional check, recommended by Muszyński [19], was placed between the questions on the questionnaire. The question was, “Were you born on February 30?” and did not differ in design or structure from the other questions in the questionnaire. The accepted answer to this question was only “definitely not”. The use of this question excluded those who did not read the questionnaire carefully from the analysis. Finally, the participants were thanked, and the correct answers to the opioid knowledge test were presented.

■ Results

The survey was completed by 686 persons, of whom 412 were eligible for analysis after excluding those who did not meet the eligibility criteria (Table I). Data was analysed using R programming
language. The mean age of participants was 27.36 years (SD = 8.62). One participant entered their age incorrectly, and this value was excluded from age-related analyses. Of the sample, 59.47% (n = 245) were female and 36.65% (n = 151) were male (Table II). Most respondents had completed higher education (42.23%, n = 174) or were currently studying (34.7%, n = 143). Information on vocational education was not collected due to an oversight in the questionnaire.

Nearly 80% of participants (79.6%, n = 328) reported having used at least one psychoactive substance during their lifetime apart from nicotine, caffeine, alcohol, and medications taken as prescribed (Table III). The most used substance was cannabis (n = 311), followed by stimulants (n = 221) and psychedelics (n = 214).

Results for the Disgust Sensitivity (DS) subscales are reported in Table IV, while correlations between the individual subscales are presented in Table V. The median score on the disgust sensiti­vity scale was 113 (IQR = 29). The median scores for the subscales were: animal-reminder disgust 24 (IQR = 14), contamination disgust 36 (IQR = 11) and core disgust 53 (IQR = 14). Consistent with the Polish adaptation of this questionnaire [8], women were more sensitive to disgust than men (U = 26902, p < 0.001). The Shapiro-Wilk test was used to assess the normality of the distributions. Results indicated significant departures from normality for the core disgust (W = 0.99, p = 0.006), animal-reminder disgust (W = 0.98, p < 0.001) and contamination disgust (W = 0.99, p = 0.025) subscales, while the total disgust score did not deviate significantly from normality (W = 1.00, p = 0.596).

Verification of hypotheses

First hypothesis

The level of social distance towards people using morphine will differ depending on the form of use, being highest for individuals addicted to intravenous morphine, intermediate oral morphine, and lowest for individuals taking morphine for medical purposes. 

The median social distance toward intravenous and oral use was nearly identical (21 for intravenous use and 22 for oral use), whereas social distance toward medical use was lower (14; Table VI). Due to the non-normal distribution of the social distance variable in the oral (W = 0.98, p = 0.023) and medical (W = 0.93, p < 0.001) conditions, as well as the non-random sampling, a non-parametric Kruskal-Wallis test was used to examine differences in social distance toward three groups of morphine users: two depending on the route of admi­nistration (intravenous, oral) and third for medical purpose users.

The Kruskal-Wallis test indicated a significant difference between at least two groups (c² = 105.42, df = 2, p < 0.001, η² = 0.25). Post hoc pairwise comparisons were conducted using Dunn’s test with Bonferroni correction to account for multiple comparisons. This correction allows all three groups to be analysed simultaneously while controlling the risk of Type I error. The η² value indicates that the route of administration explained 25% of the variance in social distance. 

Significant differences were detected between social distance toward medical and intravenous group users (Z = 8.98, padj < 0.001, r = 0.44) as well as between medical and oral group users (Z = –8.86, padj < 0.001, r = 0.44). No significant difference was observed between intravenous and oral morphine users (Z = 0.15, padj = 1, r = 0.01). Although social distance was lowest in the case of medical use, the first hypothesis that distance would be greater for intravenous use compared to oral use was not confirmed.

Second hypothesis

The higher the sensitivity to disgust, the greater the social distance towards morphine users (two routes of administration and medical use). 

We conducted Spearman correlation analyses to examine the relationships between social distance toward different routes of administration and disgust sensitivity, including its subscales. Spearman correlation was used due to violations of the assumptions for Pearson correlation (non-normal distributions and non-random sampling). 

Total disgust sensitivity was positively correlated with social distance for two routes of admi­nistration and medical use, indicating that higher disgust sensitivity is associated with greater social distance. Thus, the second hypothesis was confirmed.

For intravenous use, only the core disgust subscale was significantly correlated with social distance (ρ = 0.24, p = 0.005) and with total disgust sensitivity (ρ = 0.18, p = 0.040). For medical use, total disgust sensitivity was positively correlated with social distance (ρ = 0.26, p = 0.003), whereas the core disgust subscale was not significantly correlated (ρ = 0.14, p = 0.102). Additionally, sensitivity to core disgust was significantly correlated with social distance toward both intravenous (ρ = 0.24, p = 0.005) and oral non-medical use (ρ = 0.25, p = 0.003). For oral non-medical use, all disgust subscales were significantly correlated with social distance (Table VII). 

To examine the relationships between conditions, disgust sensitivity subscales, and social distance, linear regression analyses with interactions between condition and each disgust subscale were conducted. The assumptions of linear regression were evaluated. The Breusch-Pagan test did not indicate significant heteroscedasticity (BP = 13.40, df = 11, p = 0.268), suggesting constant variance of residuals. The Shapiro-Wilk test revealed a slight deviation from normality in the residuals (W = 0.989, p = 0.003); however, with a large sample size (n = 412), this deviation is unlikely to substantially affect the reliability of the results. Multicollinearity in the regression model with interactions was assessed using variance inflation factors (VIFs) computed with the type = “predictor” option. All the adjusted VIF values were below 3 which indicate no problematic multicollinearity among the predictors.

The regression model was significant (F(11, 400) = 17.58, p < 0.001) and explained approxi­mately 31% of the variance in social distance (R² = 0.326, Adjusted R² = 0.307). Significant interactions between condition and disgust subscales were further examined using simple slopes analysis. Analysis of simple slopes showed that the relationship between core disgust and distance was significant only in the intravenous condition (b = 0.17, p = 0.044). In the case of animal-reminder disgust, significant positive slopes occurred in the medical (b = 0.20, p = 0.005) and oral (b = 0.15, p = 0.044) conditions, while in the intravenous condition the relationship was not significant. Contamination disgust was not a significant predictor of social distance in any of the three conditions.

■ Discussion

As expected, participants reported a greater social distance toward individuals dependent to morphine compared to medical users. These findings are consistent with previous research highlighting strong biases against people with addiction [3-5, 20]. 

The results also indicate no significant differences in social distance toward individuals dependent to intravenous versus oral morphine, contradicting the prediction that intravenous use would be associated with greater social distance. This prediction was based on four considerations. First, intravenous administration is typically reserved for individuals with severe dependence [21]. Second, it carries the highest risk of infection and overdose [21]. Third, injecting psychoactive substances is associated with a higher incidence of criminal behaviour [21]. Fourth, injections may evoke stronger emotional responses as it involves penetration of the body. 

Several factors may explain the lack of a significant difference between these conditions. Individuals dependent to morphine may be perceived negatively regardless of the route of administration, and a less invasive method of administration does not necessarily reduce stigma. Additionally, in the scenario, the character was depicted as purchasing only uncontaminated morphine, which may have conveyed a sense of responsibility despite their addiction. Finally, because heroin is the most associated opioid with injection, morphine dependence may be perceived as less severe or less stigmatised. 

Sensitivity to disgust, calculated as the total score across all questionnaire subscales, was significantly and positively correlated with social distance in all conditions. Previous research has shown that higher disgust sensitivity is associated with greater social distance toward individuals who violate social norms [12, 13]. Animal- reminder disgust may additionally play a role, as it highlights human vulnerability, which may be particularly relevant when considering individuals with medical problems.

Simple-slopes analyses revealed that core disgust
sensitivity predicted greater social distance toward intravenous use. Core disgust is typically elicited by spoiled food and bodily secretions, suggesting that this type of disgust may have been triggered by the story scenarios. The core disgust scale includes items such as feelings of disgust toward vomiting, bad breath, the smell of urine in an underground tunnel, or the proximity of someone with strong body odour. These items may be more closely associated with the stereotypical image of someone dependent to intravenously administered opioids. This suggests that intravenous dependence may be perceived less as a contamination risk and more as a hygiene-related issue. 

At the same time, animal-reminder disgust predicted increased social distance in both the medical-
use and oral-use conditions. Because animal-reminder disgust is related to reminders of human fragility and mortality, it is plausible that these conditions, particularly the medical condition where the individual in the scenario has health problems, elicited stronger reactions of this type. However, the reason why animal-reminder disgust also predicted social distance in the oral-use condition remains less clear, and further research is required to better understand this relationship.

Further research

For future research, it would be valuable to systematically evaluate disgust sensitivity scales and reconsider the inclusion of moral disgust. Further efforts should focus on adapting these scales to different cultural contexts, as a better understanding of cross-cultural differences in disgust is needed. Montgomery et al. [15] used the Disgust Scale–Revised (DS-R) [22], a revised version of the original Disgust Scale developed by Haidt et al. [23].
In the present study, the Disgust Sensitivity Questionnaire was employed, which is a Polish translation of the Questionnaire for the Assessment of Disgust Sensitivity (QUADS), an adaptation of the Disgust Scale for European populations. The QUADS differs from the DS-R in the number of items it includes (QUADS: 32 items; DS-R:
25 items). Additionally, Montgomery et al. [15] used the moral disgust subscale from the Three Domains of Disgust Scale (TDDS) [24], which was not included in this study due to the lack of
a Polish version. Unifying disgust scales could be particularly useful in research on obsessive–compulsive disorder, where disgust, sometimes including moral disgust, often plays a crucial role. 

To further investigate the relationship between disgust and attitudes toward people who use psychoactive substances, it would be valuable to include questionnaires assessing injection-related fear, such as the Injecting Phobia Scale–Anxiety [25], as well as instruments measuring overall attitudes toward drug users, such as Singleton’s scale [26], which was used by Montgomery et al. [15]. Singleton’s scale includes items addressing, for example whether individuals with dependence deserve compassion or care, and whether dependence is viewed because of weak will or as a disease. Translating these scales into Polish would facilitate additional research on prejudices, particularly toward intravenous drug users. 

Building on the study by Montgomery et al. [15], future research could employ the Implicit Association Test (IAT) in Polish contexts. The study could also be expanded to examine different oral or intranasal substance administration routes. However, it may be preferable to focus primarily on explicit attitudes, as some researchers consider implicit measures to be less reliable [27]. Assessing explicit attitudes would allow for a clearer evaluation of participants’ opinions about substance users, for example in relation to access to substitution treatment. Implicit measures could then serve as a supplementary tool. 

Future research should also consider the diver­sity of addictions. Current studies often do not specify the type of addiction, yet there are notable differences in the stigmatisation of psychoactive substances like between cannabis and heroin [28]. It would also be valuable to examine opioids used intravenously for medical purposes as well as opioids taken as part of substitution therapy, and to include a control condition in which indivi­duals take intravenous or oral medication that does not contain psychoactive substances. Investigating how disgust sensitivity influences prejudices toward different types of drug users could enhance understanding of the mechanisms underlying stigmatisation and identify the types of addictions in which disgust plays a role. This knowledge could inform training programmes for healthcare professionals or law enforcement officers to reduce biases toward people who use drugs.

Limitations of the study

At this point, it is important to note the most significant limitation of this study: the method of participant recruitment. The survey announcement was posted in various Facebook groups, including those where psychoactive substance use might be higher (e.g., groups for individuals interested in rave parties), groups where lower interest was expected (e.g., a Facebook group for Buddhists), and groups with average expected substance use (e.g., a student Facebook group). Because the advertisement explicitly indicated that the survey focused on psycho­active substances, it predominantly attracted parti­cipants with prior experience using such substances.
As a result, the largest response came from individuals involved in party culture, leading to a disproportionate sample of those with prior substance use. 

The study assessed only whether participants had ever used psychoactive substances, without measuring frequency or patterns of use, preventing further conclusions regarding usage intensity. Although the study aimed to exclude individuals with current or past addiction, participation relied solely on self-report, which may be unreliable as some respondents may not be aware of their addiction status. 

Another limitation of the study is that the scenarios used were not highly detailed. While this may have helped to minimise potential confounding factors, it may also have rendered the stories less realistic or convincing. Participants evaluated a specific individual in the scenario (a man named Jan), which could have influenced their perceptions; different results might have been obtained if the character had been of another gender. Additionally, in the study, participants were informed that Jan used the same substance in all conditions (pure, medically used morphine), which may not reflect the more diverse and potentially riskier forms of psychoactive substance use. This would also indicate that the negative perception of addiction can be influenced by providing drug users with sterile conditions and safe substances.

■ Conclusions

The results of the study indicate that disgust sensitivity is positively associated with social distance across two routes of administration use and medical use. No significant difference was observed in social distance between individuals using morphine orally versus intravenously, although both groups elicited greater social distance than the medical-use condition. Analysis of the disgust sensitivity subscales highlights the role of core disgust, which is associated with increased social distance in the intravenous condition but with lower social distance in the medical-use condition. In contrast, higher animal-reminder disgust sensitivity is linked to greater social distance in the medical-use condition. 

Despite these findings, the study has several limitations, and further research is needed to clarify these relationships. Additional work is required to refine and validate disgust sensitivity scales for use in diverse cultural and research contexts.

Acknowledgments/Podziękowania

Special thanks to Iwona Dudek for her support in preparing this paper.

Conflict of interest/Konflikt interesów

None declared./Nie występuje. 

Financial support/Finansowanie

None declared./Nie zadeklarowano.

Ethics/Etyka

The work described in this article has been carried out in accordance with the Code of Ethics of the World Medical Association (Declaration of Helsinki) on medical research involving human subjects, Uniform Requirements for manuscripts submitted to biomedical journals and the ethical principles defined in the Farmington Consensus of 1997. 

Treści przedstawione w pracy są zgodne z zasadami Deklaracji Helsińskiej odnoszącymi się do badań z udziałem ludzi, ujednoliconymi wymaganiami dla czasopism biomedycznych oraz z zasadami etycznymi określonymi w Porozumieniu z Farmington w 1997 roku.

References/Piśmiennictwo