Response A to: “The impact of New Zealand’s 2018 methamphetamine policy on residential contamination”

Dear Editor,

The recent article in the New Zealand Medical Journal, “The impact of New Zealand’s 2018 methamphetamine policy on residential contamination”, frames the decision to relax methamphetamine testing thresholds as associated with a “substantial” rise in residential contamination.¹ The article was picked up by the media, with headlines linking the policy to the risk of health harms to children. Although methamphetamine-related contamination is worth taking seriously, the paper’s conclusions and recommendations are not well substantiated by the evidence presented, and this matters for how the public and policymakers should read it.

The article opens by asserting that methamphetamine use “substantially increases” crime, child maltreatment, road crashes, mortality and healthcare costs, citing a run of studies that largely comment on or establish association, not causation. This use of causal language is apparent across the article. The study’s own conclusion links its findings directly to premature deaths, child maltreatment and healthcare costs, in relation to passive methamphetamine exposure, while largely failing to comment on the general lack of evidence related to this issue specifically, and not collecting health outcome data whatsoever. Furthermore, nowhere is methamphetamine use situated within the wider socio-economic or structural context of Aotearoa New Zealand in which drug-related harm typically occurs; an omission that matters because drug use, including methamphetamine use, does not inevitably lead to harm, whether that be harm to self or to others.

Citation issues compound this problem. One study of children removed from active clandestine drug-manufacturing laboratories is used to support a claim about passive exposure more generally.² Elsewhere, the paper attributes a proposed threshold framework to a 2019 paper that does not propose thresholds.³ These figures are likely related to a 2016 Institute of Environmental Science and Research (ESR) risk assessment,⁴ which proposed lower remediation targets, and to the subsequently published NZS8510:2017 standard for methamphetamine-related remediation.⁵ However, neither the 2016 report nor the standard is engaged with directly, and subsequent 2020 and 2022 ESR reports that explicitly discuss the 15mcg/100cm² threshold are absent from the article.^6,7

The statistical case is also thinner than the framing suggests. The core result, a fixed-effects estimate of an average increase, comes from a pre-post comparison of a select number of homes. The paper cites rising national methamphetamine consumption, including wastewater-based data, as background, but this is not incorporated into the model, despite having the means to do so. As the authors point out in their abstract and results, the model indicates association only and thus cannot distinguish a genuine policy effect from any potential upwards trend in consumption at national or regional levels. Several other important issues further limit the study, such as voluntary testing after 2018, which is likely to have altered which properties were tested, independent of any real change in contamination. Furthermore, the data used are non-random and include only a select number of homes tested before and after the policy change. No sensitivity analyses were described, raising the question of whether a small number of outliers may have materially influenced the result.

Importantly, the report that precipitated the 2018 policy change concluded there was no evidence of harm from passive methamphetamine exposure at any level, and that a 30-fold safety margin remained even after the threshold was raised to 15mcg/100cm².⁸ This is mentioned but never substantively engaged with regarding the findings, despite the paper’s framing relying on implied health risk of passive exposure in homes. Importantly, the 1.93mcg/100cm² increase on top of the pre-policy mean (5.71mcg/100cm²), or the less conservative post-policy mean of 7.18mcg/100cm², both situate contamination below half the 15mcg/100cm² threshold on average across the sample, a fact the paper does not discuss, despite suggesting the change is likely to increase future healthcare costs.

The presence of these issues does not mean that the underlying question is unimportant, or that no change occurred. As of 2026, Aotearoa New Zealand operates under formal regulations built around the 15mcg/100cm² threshold,⁹ without major evidence that suggests this level is unacceptable due to health risks associated with passive exposure to methamphetamine. Any article suggesting change to the relevant national policy deserves scrutiny given the history of this debate and the potential consequences for health, housing and people who use drugs. If policy change were to be made based on potentially limited or flawed evidence, there are significant potential impacts. These include the cost of remediation, an impact on tenancies, potential child protection issues and stigma for families. This emphasises the need for a robust evidence base before considering policy change.

In this fiscally constrained environment, when many health programmes are under significant financial strain, the imperative to invest public money wisely becomes greater. This includes increased investment in treatment, prevention and harm reduction services, particularly those that address the underlying determinants of health, reduce inequities and have strong evidence of efficacy.¹⁰

Ngā mihi, nā
Jai Whelan, Joseph Boden and Rose Crossin