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

To the Editor of the New Zealand Medical Journal,

I am writing on behalf of The New Zealand Drug Foundation Te Puna Whakaiti Pāmamae Kai Whakapiri in relation to the article by Irfan et al., “The impact of New Zealand’s 2018 methamphetamine policy on residential contamination”,¹ published in the New Zealand Medical Journal’s 14 August 2026 issue.

I note that the article’s methods section states “Data for this study were obtained from testing laboratories and compiled at Safe & Healthy Home Solutions [SSHS], New Zealand”, and the acknowledgements thank SHHS “for sharing laboratory test data”. Despite this, the competing interests statement reads: “The authors have no relevant financial or non-financial interests to disclose.”

I note that publicly accessible information suggests that one of the authors, Ushan Indika Goonawardane, has held two consecutive roles at SSHS since July 2024—business analyst intern and his current role as strategic management consultant (full-time, November 2025–present). This indicates that the co-author has an ongoing relationship with the paper’s sole data-providing organisation at the time the article was prepared and published.

SHHS (which also trades as MethSolutions) is a commercial methamphetamine testing provider. The company’s revenue is contingent on the volume of testing commissioned by property owners and landlords in New Zealand. This is particularly problematic as the article’s central finding and policy recommendations include reversing the 2018 threshold change, adopting lower contamination thresholds and subsidising testing to ensure the sufficient take-up of testing services. If adopted, these changes would directly benefit the commercial interests of SSHS.

We believe that this relationship would meet the threshold for “disclosure” under the International Committee of Medical Journal Editors’ recommendations on “conflicts of interest”—of which the New Zealand Medical Journal is listed as a member.² This conflict should have been reported regardless of whether any author holds a personal or financial position within SHHS. Further to this, we also note the Journal’s own long-standing guidance to authors that asks that readers “know whether there is any financial or other conflict of interest which may have biased the work”. This standard is broader than direct financial interests and we believe that the aforementioned undisclosed relationship is in contrast with this statement.

This is not a critique of the data source alone. We note that the authors are transparent in their limitations section about the non-randomised and self-selected nature of the samples analysed. However, our concern is that the paper is reliant on a single, commercially interested data provider that is not clearly outlined as a conflict of interest. Readers, policymakers and media cannot weigh the paper’s conclusions appropriately without that disclosure.

In addition to these concerns, we would also like to draw the Journal’s attention to related matters that compound our concerns around the significance of this omission.

1. The paper’s fixed-effects model controls only for time-invariant property characteristics and does not distinguish the actual effects of the 2018 policy change from the rising methamphetamine consumption over the same multi-year window. However, the abstract and conclusion present the association as if it supports a causal claim associated with the policy change.
2. The paper presents a policy recommendation for more testing to reduce health harms associated with third-hand methamphetamine exposure. However, all the evidence of these harms cited in the report are from studies that have been significantly critiqued and fail to clearly illustrate the actual health impacts and their causal relationship to methamphetamine contamination levels.
3. The report claims that clandestine manufacturing has “increased” by citing the 2023 Bogun et al. report, whose dataset ends in 2021. The paper itself attributes part of the observed trend to COVID-19, rather than more recent or representative trends in domestic manufacture.

In terms of resolving these concerns, we are not asking the Journal to posit the authors’ intentions. Our request is that that New Zealand Medical Journal:

1. Request that the authors submit a corrected version of the article that includes a competing interest statement disclosing the co-author’s relationship with SHHS. We also suggest a competing interest disclosure of the data provision relationship with SHHS as an entity with competing interests in increasing methamphetamine testing and subsidised government testing.
2. Consider whether the methodological limitations outlined above, taken together with the undisclosed relationship, warrant a wider editorial review of the article.

We welcome the opportunity to discuss this further or provide additional information should that assist the Journal’s decision on this matter.

Ngā mihi,
Sarah Helm