Factors That Influence the Effectiveness of Primary Prevention of Substance Use: A Review of Reviews

1.1. The Public Health Model

The priorities of this model include keeping the target group abstinent, decreasing the incidence of substance use, and avoiding dependence in cases that substances are being used (28-30). This approach identifies three categories of intervention.

1.2. Risk and Protective Approaches

The focus of this model is on controlling the risk factors and promoting the protective factors. As people exposed to risk conditions do not necessarily start to use substances or become dependent, both risk and protective factors can be different from one person to another (24, 27, 31). Furthermore, risk and protective factors depend on demographic characteristics such as age, gender, race, and culture (27). Intervention programs based on this approach focus on the improvement of self-efficacy, decision-making, communication skills, life skills, resistance against peer pressure, resilience, and awareness about substance use and its consequences (24, 25, 27, 30).

(1) Risk factors depend on psychological, social, biological, environmental, and behavioral elements that have the potential of being the source of health problems and, therefore, an underlying cause for substance use (18, 24, 27).

(2) Protective factors include all conditions that reduce or prevent the possibility of using substances (27, 32).

1.3. Communicable Disease Model

This model consists of a triangular arrangement of elements, ie, (a) the host, (b) the agent, and (c) the environment. According to this model, the objective of prevention programs is to block the effects of the agent on the host, either directly or through modifications in the environment. Examples of this approach include keeping schools free of substances, smoke-free schools, and taxation on alcohol sales (24, 27, 30).

1.4. Context-based Setting of Interventions

The focus of this approach is on the setting where the intervention is provided and the context of this setting that might influence the intervention and its effects (27, 29).

4.1. The Results for School-based Prevention Interventions

The results obtained in this setting were extracted from 26 articles (Appendices 1 - 4) (25, 42, 45-68). The results of school-based prevention interventions for tobacco, alcohol, cannabis, and substance and drugs are available in Appendices 1 – 4 (see Supplementary File).

4.2. The Results for Family-based Prevention Interventions

The results obtained in this setting are extracted from 13 articles (Appendices 5 - 8) (25, 41, 47, 50, 51, 60, 66, 69-74). The results of family-based prevention interventions for tobacco, alcohol, cannabis, and substance and drugs are available in Appendices 5 - 8 (see Supplementary File).

4.3. The Results for Community-based Prevention Interventions

The results obtained in this setting were extracted from one systematic review article for tobacco, as well as from two overview of reviews articles for substance (Appendix 9) (25, 41, 71). The results of community -based prevention interventions for tobacco are available in Appendix 9 (see Supplementary File). There were no data available from 2009 to 2019 on community-based prevention interventions for alcohol, cannabis, and drugs.

4.4. The Results for Technology-based Prevention Interventions

The data obtained in this setting were gathered from six studies (Tables 2 and 3) (25, 35, 36, 67, 75, 76). There were no data available from 2009 to 2019 on technology-based preventive interventions for Tobacco and Cannabis.

5.1. Types of Interventions

Compared to other types of interventions, universal interventions were more likely to be effective, irrespective of setting, age, and substance type. In specific instances such as school-based interventions, uni-modal targets programs have been reported to be effective for cannabis use. In one school-based review (61) more than 70 percent of the studies were universal, about 18 percent were selective, and 9 percent were indicated. Forty-three (out of 30) articles of the reviews were on "universal studies", two were on "selective studies", another two were on "indicated studies", and five were collective studies of all tree intervention types, the rest of the studies were reviews on reviews. An explanation for the wider practice of universal prevention programs might be their less costliness and coverage of larger populations. One would also think that universal programs are easier to perform due to the less complex nature of a universal program compared to other types that need to further be tailored for specific groups. Therefore, the higher reported effectiveness of this type of prevention needs to be adjusted by their frequency of practice.

Selective intervention programs have been reported to be effective in the family and in technology-based settings. While no data is available for selective interventions in early age groups, it has been reported to be effective in adulthood (ages 19 and above). Although universal interventions are reported to be relatively effective in white target groups and only for alcohol and tobacco, it appears that selective and indicated interventions are effective in the reduction of cannabis use (77). Furthermore, selective and indicated interventions have resulted in the more frequent use of social services by families, increased knowledge of parents about substances, and reduced aggressive behaviors (77). A majority of the studies have reported that universal interventions to be less effective in the family setting (73). Perhaps this difference is a result of the variety of target groups in universal interventions compared to selective and indicated interventions. Where selective programs concentrate not only on parents and could involve both the family and children, universal interventions mostly focus on the parents alone.

Selective studies, which generally focus on family relationships (FR) and positive parenting (PP), have been investigated by meta-analyses. Moreover, the higher incidence of effective selective and indicated prevention programs in family settings can also be attributed to the fact that universal programs reflect a higher level of heterogeneity and thus measuring their effectiveness is more difficult by meta-analysis studies, which in turn translates into underreported (73, 74).

When provided to those older than 19 years, selective interventions that follow a technology-based model are more effective. Such interventions, however, have commonly been performed to reduce or regulate the use of alcohol in universities and did not target total abstinence. In other words, brief intervention and short-term motivational interviews are mostly intended to reduce harm, rather than primary prevention (67). This finding leads to the impression that perhaps limited or non-effectiveness of primary prevention programs for alcohol is related to the legalized status of the substance. For comparison, we found that while the availability of cannabis in countries where it is legalized has not been shown to result in increased use, universal interventions have also been shown to be non-effective when compared to a control group (78). Therefore, it can be argued that universal, but not selective interventions, are not effective against legalized substances. In the case of smoking, however, that is also legalized, universal primary prevention has shown to be effective. Perhaps the difference between cigarette smoking, as a legal substance, and alcohol and cannabis is about their attitudinal difference. While it is widely accepted that smoking has severe negative consequences, in the case of alcohol and cannabis, there is a common belief that they have at least some benefits.

5.2. Theoretical Models

Although limited or no reports are available on interventions designed based on a social model for other substances, they are effective when used for tobacco prevention. More specifically, social learning-based interventions designed for school settings for those aged 11 to 18 years and those designed for community settings with the target group of older than 11 are shown to be effective. One, therefore, could say that interventions based on the social learning model, regardless of the age of the target group, are effective. Although the social learning model has been criticized for providing the role modeling of substance use behavior, rather than abstaining, our review showed that when social learning programs include negative consequences of substances, the desired effect of not initiating substances outweighs the unwanted learning of the behavior of using substances. Furthermore, self-efficacy and self-belief in one's abilities can also have positive effects on substance use prevention, despite being exposed to parents and peers who use substances.

It has been shown that health education-based interventions provided to those aged 11 to 18 years old can be effective in school settings. Likewise, interventions based on social competence are also shown to be effective in the age group of 11 - 18, when performed in a school context. However, neither of the two models have shown to be effective in the age group of 5 - 10 as long as they are performed exclusively. Yet, when health education was combined with social-competence or social-influence programs in a school context the objective of primary prevention is achieved. Interventions based on health education are not limited to the prevention of alcohol and substances and have effectively been used for the prevention of violence, high-risk sexual behaviors, and delinquent behaviors either combined with substance use prevention or else.

The commonly observed effectiveness of health education models in school settings is a reminder of the above-mentioned observation that universal models have generally been shown to be effective when performed in a school setting. The effectiveness of universal models in school settings might be attributed to different factors including (a) the presumption and receptive preparedness of students for being exposed to new ideas in schools; (b) interaction with peers for shaping permanent social and behavioral characteristics is at its highest capacity during school age; (c) the school and its programs are considered as a template for social norms and values by students; (d) the students are prepared to face and accept new rules and regulations; (e) prescreening of school staff for appropriate behaviors and background provides a more acceptable social milieu of role models who already follow the contents and objectives of prevention programs; and (f) compared to selective and indicated substance use interventions that commonly result in stigmatization of the target group, the comprehensive and buffering nature of the school prevents the students from such consequence.

Interestingly, universal models seem to be less effective or ineffective in the age group of 5 - 10, even in a school setting. The observation that health education programs are not effective in the age group of 5 - 10 reveals the fact that if the effect of health education is by the means of fear of death, this won't be the case for the age group that has not yet formulated a general concept of death. Another explanation is focused on the bright side of health and promoted health conditions that result in better fulfillment of life. In addition, it is also an advanced concept that is difficult to understand for 5 - 10 years old children. Moreover, it has been observed that in the age group of 5 - 10, interventions based on the social influence that are performed either in a school context or a community setting cannot be effective alone and only show effectiveness when they are combined with other models such as health education or social competence. The reason that the solo model is not effective in students aged 5 - 10 years could again be a result of an age-related psychological development.

Compared to selective programs, universal programs are less complicated to perform. Therefore, in family settings, one would expect a more frequent practice of universal programs. This was not, however, shown in systematic reviews included in this study. By definition, when the family is not problematic, substance use prevention would become a universal category intervention. Interestingly, it appears that parents are less motivated to participate in universal prevention programs (74). This lack of interest of parents from non-problematic families might reflect their concern that by participation in substance use prevention programs and by being exposed to new information about substances, their children might become more vulnerable to using substances. Universal interventions intended to prevent alcohol consumption are an exception to this pattern. It appears that as alcohol use is normal behavior and parents would logically anticipate the potential for alcohol consumption to become problematic for their children in the future, they actively participate in such programs, which translates into the effectiveness of the program (79).

The information model and problem-solving have been less effective when exclusively performed in a family setting. However, interventions focusing on family relations and bonding have been reported to be effective when performed in family settings; a condition that fits under the category of selective interventions. Therefore, one may conclude that although universal interventions are more or less effective in different intervention settings when performed in the family setting, they appear to be less effective (73). Aside from universal programs, selective programs focused on problem-solving were also shown to be less effective. It appears that, much further to the skills training in those programs, problem-solving is influenced by a wide range of social and cultural factors from the background. Perhaps the lack of coverage of high heterogeneity of such social and cultural factors in problematic families has played a role in selective programs being less effective (74).

3.3. Duration of Interventions

The school setting seems to be an attractive context to prevention researchers. Therefore, a wide range of prevention programs with different durations have been performed in that setting. However, we couldn't identify any association between duration of intervention and effectiveness of programs reported in systematic reviews; hence, keeping the field open to future exquisite duration-based effectiveness studies. Interestingly, some systematic reviews found an inverse relationship between the duration of programs and their effectiveness. However, this pattern was not examined by meta-analyses. Therefore, the validity of such descriptions by systematic reviews needs further examination. Discussing the duration of interventions and follow-up of their effects, the literature is silent on optimal dose-duration of prevention programs. There is also a lack of reference to the expected durability of effects of an intervention, with an unproven implicit assumption that repeated boosters will continuously keep the effects alive. Perhaps based on age group and other related factors, a person needs different types of substance use preventions in different settings throughout one's phases of life. The observation that in those older than 18 it is the indicated prevention program type with a higher focus on harm reduction with more effectiveness is a sign of the age-related transformation of prevention needs. In general, the factor of duration in substance use prevention, so far, seems to suffer from adequate substance.

3.4. Providers of Interventions

Interventions were more effective in most contexts only when they provided by a specialist or a trained person who was an external educator to the intervention setting. In school and family settings, prevention interventions were shown to be more effective when provided directly by a specialist or by specialists accompanied by usual providers such as teachers. Interventions with a combined approach of family-based and computer-based were more effective than unparalleled approaches. Alcohol prevention programs for those older than 18 were effective either when performed on a long-term basis and provided in person by a specialist or when they were short-term but computer-based. When interventions were provided on a co-provider basis such as combinations of specialist-teacher, peer-teacher, teacher-parents, and specialist-parents, they were more effective than when provided by single providers. A reverse effect is reported (ie, increased substance use) for interventions focused on high-risk youth that are provided solely by peers. The observation on providers of prevention programs shows that prevention programs require higher knowledge and skills and may not be left to untrained lay providers. In addition to expert skills, the observation that a co-provider model increases the effectiveness of the program leads to an impression that the presence of a co-provider increases the internal consistency and structured format of the intervention. The fact that computer-based programs showed significant effectiveness, even in interventions with shorter durations, might reflect the role of internal consistency and structural orderliness of interventions, which is a key feature of computer-based programs (80, 81).

Our study revealed that in some important areas, such as universal interventions in family settings and in those aged more than 18, community-based interventions intended to prevent alcohol and cannabis, and technology-based intervention designed to prevent tobacco and cannabis, there is a scarcity of evidence, particularly during the past decade. The school setting is the most common context used for the implementation of substance use prevention programs with effective outcomes. However, the school setting is now in a transitional phase of replacing much in-person training with online programs. It is, therefore, important to think and study alternatives to this effective context for the future. Another suffering of the substance use prevention literature, as reflected in most systematic reviews, is the high heterogeneity of the studies. Therefore, most of such reviews did not provide a meta-analysis with common denominators on the effectiveness of interventions. We, therefore, suggest the need for further classification of preventive studies such as the template we used in our study.

Evaluating the effectiveness of substance use prevention programs is difficult because their evaluation should be according to the time frame that participants face the risk of substance use or the settings where substance use is at higher risk. Therefore, many short-term effectiveness evaluations of substance use prevention interventions are far from strong evidence. Even with this shortcoming, effectiveness studies are not yet standardized. We have proposed a template that can be used to increase comparability and homogeneity of effectiveness studies.