The impact of New Zealand’s 2018 methamphetamine policy on residential contamination

It is globally recognised that methamphetamine is an extremely addictive psychoactive stimulant that can cause severe health and societal damage. The use of methamphetamine substantially increases crime,¹ child maltreatment,² road crashes,³ premature mortality⁴ and healthcare costs.⁵ Almost 110 countries have reported the use of methamphetamine, and its related harm has been more prevalent in the United States of America (USA), Mexico, South Africa, Asia, Australia, New Zealand and Europe.⁶ The adverse effects of methamphetamine consumption are not limited to direct users; methamphetamine also impacts individuals through passive exposure.⁷

The clandestine manufacturing and use of methamphetamine can contaminate residential properties for a long period of time, which eventually affects the health of residents, particularly children.² Methamphetamine production in clandestine laboratories at residential properties usually results in much higher levels of contamination compared with smoking.^8,9 In addition, even after methamphetamine has been manufactured, the risk of passive inhalation remains significant.⁹ Policymakers are struggling to identify a level of methamphetamine contamination on household surfaces that minimises risk to human health. So far, only Australia, New Zealand and the USA have developed and promulgated policies for reducing the negative health impacts of methamphetamine contamination.¹⁰ For instance, in all states and territories of Australia, 0.5mcg/100cm² is the threshold for residues from manufacturing or clandestine laboratory sites. Residential properties below that level are not obligated to be remediated, while those above require remediation.¹¹ Similarly, in the USA, the threshold for remediation varies from state to state, between 0.05 and 1.5mcg/100cm².¹²

New Zealand’s methamphetamine contamination policy has undergone many changes and remains the topic of ongoing debate.¹³ For instance, in 2010, based on the established Australian guidelines and the Ministry of Health – Manatū Hauora’s advice, New Zealand adopted a methamphetamine contamination housing policy and set a threshold level of 0.5mcg/100cm².¹⁴ The real estate industry, local councils, the Tenancy Tribunal and Housing New Zealand (now Kāinga Ora) began to apply this threshold level. In 2018, following a change in government, the residential properties methamphetamine contamination policy was reviewed, and resultantly the threshold level was increased to 15mcg/100cm².¹⁵ This policy change was recommended because the risk assessment committee primarily indicated that methamphetamine contamination levels below 15mcg/100cm² are unlikely to pose a significant health risk; consequently, testing is advised mainly for households with heavy methamphetamine use or methamphetamine manufacturing.^13,15 The policy change was implemented in May 2018, and consequently many private and public stakeholders became less concerned about methamphetamine contamination. However, the Institute of Environmental Science and Research (now the New Zealand Institute for Public Health and Forensic Science), a crown research institute of New Zealand, examined international guidelines in 2019. The Institute proposed a threshold level of 1.5mcg/100cm² for general high-use areas in a dwelling (such as bedroom, lounge, kitchen and hallway) and 3.8mcg/100cm² for limited-use areas (crawl space, shed and dining room)¹⁶—which had not been adopted as of December 2025.

The increase in the methamphetamine contamination threshold level in 2018 is significantly higher than in other developed countries (USA, United Kingdom, Australia).¹⁰ In addition, according to the New Zealand Drug Foundation, methamphetamine consumption has been increasing over time. Worryingly, in 2023/2024, methamphetamine consumption increased by roughly 19% compared with 2021/2022, and its consumption is also higher than that of other illicit drugs,¹⁷ as shown in Figure 1.

View Figure 1, Table 1–2.

Moreover, the number of clandestine laboratories for methamphetamine manufacturing increased in New Zealand between 2009 and 2021,¹⁸ and according to wastewater-based drug testing, mean methamphetamine consumption in New Zealand was higher (724mg/1,000 people per day) than other illicit drugs.¹⁹ Furthermore, according to New Zealand’s recent Drug Trends Survey 2025,²⁰ the use of methamphetamine is still increasing. Given the potential ill impacts of methamphetamine contamination stated earlier, this research investigates the impact of the policy change on the level of methamphetamine contamination in residential properties in New Zealand.

Methods

Data for this study were obtained from testing laboratories and compiled at Safe & Healthy Home Solutions, New Zealand. The dataset contains methamphetamine contamination test results for tests conducted on residential properties across New Zealand. We limited the sample to 423 residential properties that were tested both before and after the policy change, ensuring the same properties were observed across the period from January 2016 to August 2022. While the sample represents the same properties over time, contamination is not assumed to be static, as properties may be re-contaminated following changes in occupancy or continued methamphetamine use, particularly in settings with high turnover, such as rental or short-term stay properties.

For each test, the data include the methamphetamine contamination level (mcg/100cm²) and the date on which the test was conducted. As testing was voluntary and motivated by concerns about potential health impacts, it is likely that property owners or managers opted for testing when there was a perceived risk of methamphetamine contamination. The test procedure mainly consists of three steps: first, the testing company’s agent conducts a visual inspection of the property to identify the potential source of contamination and then, at the second stage, they use pre-moistened wipes to collect residues from surfaces such as walls, floors, door handles and furniture and then the wipes are sent to the laboratories for chemical analysis.²¹ Typically, multiple samples are collected from high-use areas on the property (one kit can sample up to five areas); the results are reported as the average of all the samples for each residence during a single inspection. If a re-test is scheduled, the same room and roughly the same surfaces are commonly used.

We applied a fixed-effects model to examine the impact of policy changes on the level of methamphetamine contamination. The outcome variable representing methamphetamine contamination levels for the property is modelled as a function of the policy change. The model controls for characteristics that do not change over time within each property, such as property size, location and access to amenities.

Ethical considerations

This study used anonymised secondary data; ethical approval was not required. No individual or identifiable information was included in the analysis, ensuring confidentiality and privacy were maintained throughout the research process.

Results and discussion

Table 1 presents summary statistics for the measured methamphetamine contamination level before and after the policy change. For the 423 properties tested, we observed the results of 551 tests before the policy change and 544 tests after the policy change. Before the policy change, the mean level of methamphetamine contamination was 3.78mcg/100cm², with a maximum of 53mcg/100cm². After the policy change, the mean level of methamphetamine contamination increased to 7.18mcg/100cm², and the maximum level of methamphetamine drastically increased to 220mcg/100cm². A t-test confirms that the mean methamphetamine contamination level is significantly higher after the policy change than before the policy change (t=−3.943, p<0.001).

A simple t-test does not account for the fact that some properties were tested multiple times before or after the policy change (or both). We overcame this by using a fixed-effects model. The results are presented in Table 2 and indicate that the implementation of the new methamphetamine policy (increasing the threshold level) is associated with a statistically significant average increase of 1.93mcg/100cm² in the methamphetamine contamination level at residential properties.

Limitations

It is important to note that this study has the following limitations. For instance, the sample is not a random sample of all residential properties in New Zealand, which presents the potential for bias. Additionally, testing companies’ sample collection methods may vary, which can result in slight differences in contamination level results. Our estimates demonstrate changes in the average level of methamphetamine contamination for properties that were tested, rather than for all residential properties or all residential properties where methamphetamine use is suspected. Sample composition and selection issues may therefore arise, as only those households anticipating a higher level of methamphetamine contamination may have been tested after the policy change. We also acknowledge that the results may be affected by omitted household-specific variables, such as the demographic and socio-economic characteristics of the occupants immediately before the contamination tests. Moreover, other factors, such as ventilation, cleaning and surface material, may also affect the level of methamphetamine contamination. Unfortunately, these variables are not available for analysis; however, future research may consider linking data from methamphetamine contamination tests to administrative data on household occupants, utilising Stats NZ Tatauranga Aotearoa’s Integrated Data Infrastructure. (Stats NZ Tatauranga Aotearoa provides datasets, including the Household Economic Survey, New Zealand Health Survey, Census and various administrative datasets, within the Integrated Data Infrastructure, which can be accessed through a formal application to Stats NZ Tatauranga Aotearoa.)

Conclusion

Curbing the production, supply and consumption of addictive stimulants such as methamphetamine remains a top priority for governments. The use of methamphetamine not only damages methamphetamine users—passive exposure to methamphetamine through residential contamination has the potential to pose serious health issues for passively exposed people, especially children.

Our results demonstrated a significant increase in methamphetamine contamination at residential properties in New Zealand between the period before and the period after a change in the threshold for remediation. The mean increase of 1.93mcg/100cm² is substantial, being a 51% increase on the pre–policy change mean level of contamination in tested properties of 3.78mcg/100cm².

The increase in methamphetamine contamination at residential properties may arise through several mechanisms. First, the rise in methamphetamine contamination level may reflect an increase in clandestine methamphetamine manufacturing laboratories in New Zealand (as Bogun et al. [2023]¹⁸ discussed in their research). This increase in production may have also caused an increase in methamphetamine consumption, reflected in higher contamination levels in residential properties. Second, the policy change may have led residents to become less vigilant about methamphetamine related risk.

It is suggested that the New Zealand government revisit the policy change and follow the lead of other developed countries in setting a lower threshold of methamphetamine contamination above which property remediation is required. The government could adopt the Institute of Environmental Science and Research’s recommended methamphetamine contamination thresholds (1.5mcg/100cm² for high-use areas and 3.8mcg/100cm² for limited-use areas in dwellings). However, we note that other commonly used methamphetamine contamination levels (0.5–1.5mcg/100cm²) are based on published quantitative health risk assessments.^11,12 Moreover, to ensure sufficient take-up of testing services, the government may also consider subsidising methamphetamine contamination tests. A lower testing cost would encourage many more homeowners and landlords to test their properties. The government should also consider including methamphetamine contamination levels within the “healthy homes standards” (https://www.govt.nz/browse/housing-and-property/insulation-and-energy-efficiency/rentals-healthy-homes-standards/) so that community health risk could be minimised. Finally, further research is needed to quantify the health impact of passive exposure (including economic and emotional costs) to methamphetamine in residential homes so that, in future, the threshold level can be set in a way that accurately accounts for the risks.