This study involved the ranking and weighting of harms from a wide range of drugs used in Aotearoa New Zealand, with an expert panel employing an established MCDA methodology. In addition to ranking drug harms for the overall population, we also undertook a separate process focused specifically on drug harm among Aotearoa New Zealand youth aged 12–17 years. This is, to the best of our knowledge, the first drug harms ranking study specific to youth. The study also modified existing criteria and included two new harm criteria to more closely reflect an Aotearoa New Zealand cultural view.

Consistent with drug harm MCDA findings for the United Kingdom (UK), European Union (EU) and Australia (Bonomo et al., 2019; Nutt et al., 2010; van Amsterdam et al., 2015b), alcohol was ranked as the most harmful drug in the overall population workshops, and in the youth-specific workshop in Aotearoa New Zealand. The issue of alcohol misuse in New Zealand is widespread, where an estimated 19% of adults, and 33% of Māori adults, drink to hazardous levels (New Zealand Ministry of Health, 2022). Many experts argue that current alcohol policy and regulations in Aotearoa New Zealand are insufficient to curb these harms and their inequitable distribution, with the annual cost of alcohol harm estimated as $7 billion (Nana, 2018). When only considering harms to self, alcohol was ranked lower in the youth MCDA, with the panel discussion focussing on an ‘average user’ of alcohol in youth, and reflecting on current consumption patterns (Fleming et al., 2020). Despite this ‘average user’ approach, it is also important to note that binge drinking among this group remains high when compared with other countries, reflecting the relative ease at which youth can access alcohol (Fleming et al., 2020). To meaningfully reduce alcohol-related harm in New Zealand, it is important to consider the major recommendations made by the New Zealand Law Commission in 2010, which are well supported by international evidence: increasing the price of alcohol via excise tax; eliminating alcohol advertising and sponsorship; reducing the density and opening hours of alcohol outlets; and increasing the age of purchase from 18 to 20 (New Zealand Law Commission, 2010). A minimum unit pricing scheme is also recommended, with this strategy having demonstrated efficacy in several countries (Franco, 2015; Hydes et al., 2019). Furthermore, with regard to inequity of harm, alcohol law and policies must also address the ongoing impacts of colonisation and the broader social determinants of health, as well as enable Māori to lead and define the way forward for them in the alcohol space.

Methamphetamine was ranked as second most harmful in the overall population and youth workshops, which reflected its significant adverse impacts upon those who use it and their communities. This high ranking was at odds with findings from the EU and UK rankings, but consistent with those of the Australian drug harms ranking study. As with Australia, Aotearoa New Zealand has a comparatively high prevalence of methamphetamine use by international standards, with use being overrepresented in areas of socio-economic deprivation, among males, and among Māori (Bax, 2021; Price et al., 2021). In contrast, Europe has lower rates of methamphetamine use, with use being largely limited to specific countries and regions (Bonomo et al., 2019). However, one key difference between the Australian and Aotearoa New Zealand MCDA findings was that the harm to others arising from methamphetamine use was significantly higher in Aotearoa New Zealand. In the overall population ranking, methamphetamine received high scores on harm to others criteria including family adversities, intergenerational harm and community harm. Factors that contributed to the high ranking of methamphetamine included its deleterious effects upon physical and mental health, high potency and associated risk of dependence, impacts on cognitive function, contribution to acquisitive and violent crime, stigmatisation, and impact upon communities (Barr et al., 2006; Boden et al., 2023; Darke et al., 2008; Deen et al., 2021; Foulds et al., 2020; McKetin et al., 2020; Potvin et al., 2018). Taken together, these findings indicate that methamphetamine use is a significant social and community issue in Aotearoa New Zealand. Several approaches have recently been recommended to address this harm, including the expansion of an existing social well-being intervention, health-harm reduction measures, and increased treatment and support for those who use methamphetamine (Yasbek et al., 2022).

For both the total population and youth, synthetic cannabinoids were rated as third most harmful overall, and as more harmful than cannabis. While improved drug checking and surveillance systems will assist in mitigating the harms associated with the rapidly evolving supply of high potency synthetic cannabinoids (Peacock et al., 2019), these drugs are likely to have ongoing appeal due to their low price, high strength and ability to avoid detection in drug tests. Thus, ongoing review of synthetic cannabinoid harm reduction measures and policy settings will be necessary. In Aotearoa New Zealand, the Psychoactive Substances Act was put in place to regulate and to assess and potentially approve new psychoactive substances including synthetic cannabinoids for legal sales (Rychert and Wilkins, 2018a; Rychert and Wilkins, 2018b); however, no psychoactive products have been approved under this framework. When considering only harms to the individual, synthetic cannabinoids and methamphetamine were ranked almost equally as being most harmful to youth who use these drugs, due to factors such as impacts on education, death from overdoses, and the impact of losing close relationships and support systems as an adolescent. It is also notable that cannabis was rated as being significantly more harmful to youth who use these drugs, relative to other drugs, than to the overall population. This difference reflects issues such as the negative psychosocial impact of early onset cannabis use in particular (Fergusson et al., 2002).

The harm scores for opioid drugs were lower than those seen in Australia, with the opioid drug groups ranking fifth or lower for the overall Aotearoa New Zealand population, compared to heroin and fentanyls in Australia that ranked third and fourth, respectively. Fentanyl was first detected as a contaminant in the Aotearoa New Zealand illicit drug market in February 2018 (Know Your Stuff, 2018); however, it is important to note that our workshops occurred prior to further detections of local use of powdered fentanyl (Heikell, 2022). Although prevalence was not considered in these workshops, the previous lack of use meant that expert knowledge on local fentanyl-related harms was limited. While the mortality risks of fentanyl were widely understood by the panel members, very limited local data may have meant that some local fentanyl-related harms, such as community damage, were less salient for our expert panel. It is essential to be prepared for these high-potency opioids increasing in the local drug market, and therefore, investment in harm reduction needs to be proactive (Ponton and George, 2020). This should include overdose prevention measures such as supervised injecting facilities and take-home naloxone programmes, both of which have extensive evidence of efficacy in reducing harm (Monds et al., 2022; Levengood et al., 2021; Tse et al., 2022). Given that Aotearoa New Zealand’s drug market may change, integrated and responsive systems for rapid surveillance, and engagement with affected communities is vital.

When comparing rankings from the youth and overall population MCDA results, several differences were apparent. The family adversity criterion was evaluated as being less significant in the youth panel than the population panel. Although drug use by young people can result in significant family adversity, including worry and conflict between family members, there were several additional features of this criterion which were more relevant to the wider population. For instance, drug use by adolescents was identified as less likely to result in issues such as child maltreatment, loss of family income due to job loss or drug purchase, or separation of families due to drug-related imprisonment. Another key difference was seen for drug-related damage, which tended to make up a higher proportion of overall harm scores in the youth workshops, relative to the overall workshops. For youth, ratings for this criterion were elevated at times due to issues such as associations between the use of some drugs and self-harm (Bresin and Mekawi, 2022), and the higher risk of self-harm among young people (Klonsky, 2007). In terms of the rankings for specific drugs, a large difference was observed for solvents and fuels, which were ranked fourth most harmful for youth, compared with tenth for the overall population. In addition to potentially causing pronounced and lasting cognitive impairment following chronic use (Dingwall and Cairney, 2011; Manikandan and Balasubramanian, 2020), solvents and fuels are more commonly used by youth who are already vulnerable, including those from lower socio-economic backgrounds and more troubled families (Dinwiddie, 1994; Kurtzman et al., 2001). For these individuals, impacts on neurological and physiological functioning may further limit opportunities such as educational attainment and associated career pathways (Real et al., 2021; Manikandan and Balasubramanian, 2020). Given these unique findings for youth, and their ability to inform specific drug harm strategies for this group, future drug harm studies should also consider the value of separately ranking harm for younger individuals.

The impact upon families and communities was pronounced for many of the drugs, including alcohol, methamphetamine, tobacco, synthetic cannabinoids and different opioid drugs. These harms encompass issues such as child abuse and neglect, problems with emotional development for children, intimate partner violence and foetal alcohol spectrum disorder (Kelley et al., 2010; Wells, 2009). In many cases, the continued purchase of drugs can result in debt, unemployment and risks to housing, while imprisonment due to drug-related crimes can lead to separation of families and loss of employment opportunities. Issues such as these may perpetuate a cycle of intergenerational harm, whether through increased likelihood of drug misuse among younger generations, loss of connection to family/whānau, or through associated adverse psychosocial outcomes. Higher rates of drug use can also lead to stigmatisation of particular communities in which drug use occurs, while internalised stigma may lead to further harm within these groups (Can and Tanrıverdi, 2015). The findings also highlighted the relevance of the two new criteria of intergenerational harm (harm to others) and non-physical/spiritual harm (harm to self) in capturing drug-related harm in Aotearoa New Zealand. For many drugs, these two criteria made up a large portion of the overall harm from a given drug. For instance, in both the youth and overall results, intergenerational harm represented one of the highest criterion contributions for several drugs, including alcohol, methamphetamine, cannabis, and tobacco. Findings from these two new criteria highlighted additional ways that many drugs can harm others and perpetuate existing difficulties arising from drug use. Considering their utility in measuring additional forms of harm, future drug harms MCDA studies may similarly choose to include these criteria in their decision matrices.

For many drugs, current policy responses contributed to higher ratings on specific criteria, with one example being criminalisation due to drug possession and use. Therefore, for drugs such as cannabis, the higher harm scores are largely a function of current drug policy settings. For those affected by drug misuse, prosecution for possession acts as an additional stressor while reducing future opportunities. Māori are disproportionally affected by criminalisation of people who use drugs; although Māori make up 17% of the population of Aotearoa New Zealand, 48% of those convicted of drug possession are Māori, demonstrating clearly that drug laws are being enforced in a racially biased manner (New Zealand Drug Foundation, 2022; Statistics New Zealand, 2021). Our recommendation is that a review of Aotearoa New Zealand’s drug policy is needed, which considers a health-based approach to managing drug use and structural determinants of drug harm, including any negative effects of the current prohibition-based drug policy. Drug-related harms and existing strategies to prevent drug availability and use also tend to impact the most vulnerable populations. Therefore, implementing evidence-based harm reduction measures, in addition to focusing on population-level risk factors, such as socio-economic deprivation, may be a more effective way of reducing drug-related harm (Holland et al., 2022).

These findings should be considered with a number of limitations in mind, some of which have been previously described in relation to the MCDA method used to rank drug harms (Nutt et al., 2010; van Amsterdam et al., 2015a; van Amsterdam et al., 2015b). Firstly, experts can only draw on available knowledge and resources, which are incomplete and limited for some drug types. For instance, for some drugs that are novel or have a lower prevalence of use within Aotearoa New Zealand, there may be incomplete data on some kinds of harm (e.g. social harms). It is possible that higher-profile harms or more prevalent drugs had more salience for the expert panel; the process relies on best-available knowledge at a given point in time. For instance, as data on ENDs/vapes are currently limited, it is possible that the ratings for this category may differ markedly in a future drug harms ranking for Aotearoa New Zealand. The process was also conducted under time pressure, meaning that decisions had to be made fairly quickly and relied heavily upon the knowledge of panel members at the time. Group decisions are inherently susceptible to social biases, and it is possible that these sources of bias influenced the evaluations, although these were perhaps limited by the facilitation process. Another potential source of bias involved the use of the overall population data as a starting point for the youth MCDA, as opposed to starting the process anew. However, this was the most practical option at the time and was also beneficial in that most youth panel members gained valuable insights during the overall population workshop. We aimed to include a wide range of expertise, but it is also likely there remained knowledge gaps that may have influenced the outcomes of the ranking exercise. For example, had there been more panel members working in areas such as opioid substitution therapy services and pain clinics, scores for the opioid categories may have been higher. Similarly, the inclusion of more first responders, such as ambulance personnel, could have increased the diversity of expertise within the panel. We did not adjust our harm to user scores by prevalence of use, which was a decision made in part because of incomplete prevalence data. Although the concept of an ‘average’ individual who uses a drug was difficult to apply at times, the investigators believed that this was the best way of avoiding a ‘worst case’ evaluation of drug harm, or only considering the harms in terms of rare outcomes that are not experienced by the majority of individuals who use them. Additionally, while a set of assumptions was established for the ranking process, discussion at times strayed away from those assumptions; nonetheless, the panel and facilitators were usually quick to reiterate those assumptions and steer the discussion accordingly.

Our findings highlight the importance of separately considering harms to young people but also have two relevant limitations. First, expert panel members needed to be at least 18 years of age due to the ethical approval for this study, meaning the workshops could not directly include the perspectives of anyone aged 12–17 years. Second, an adult construct of harm was used for these workshops, in part to facilitate comparison of results, but it is likely that drug harm is conceptualised and experienced differently by young people. Due to this, young people may place more weight on different criteria, or may identify types of harm which are not well described in the current criteria. Understanding this will be the focus of a future research project as the perspectives of young people are particularly important in guiding prevention and early intervention policy and strategies. Lastly, we note that we have not yet undertaken this process for Māori, who, as noted previously, are disproportionately subject to drug policy harms (arrest/conviction). A further step in this research will be for a Māori expert panel, which has been established, to later meet and specifically examine drug harms for Māori. The outcomes from this component of the research will be presented separately.

A broad range of harms are associated with psychoactive drug use, though the extent and nature of those harms is difficult to quantify. This study is the first local drug harms ranking study using an MCDA approach to evaluate and rank the harm arising from drugs used within Aotearoa New Zealand. It should be acknowledged that not all people who use drugs experience harm (NZ Drug Foundation; United Nations Office on Drugs and Crime, 2022). However, drugs are nonetheless associated with considerable harm for many people, and an understanding of that harm should be used to prevent or otherwise minimise the impact upon those individuals. These local results can be used to inform drug policy, funding decisions, treatment and education, and, ultimately, to reduce harm and associated inequities.