Scientific research

The research is conducted by an independent team of researchers, overseen by a Guidance and Evaluation Committee made up of professors and experts. It focuses on the effects of a closed cannabis supply chain on public health, crime and safety. The pre-measurement, carried out from September 2021 to April 2022, together with a baseline measurement in 2022, forms the basis for further research.

Research design

The study uses a quasi-experimental evaluation design, comparing the ten participating municipalities (intervention municipalities) with nine control municipalities. In the participating municipalities the cannabis experiment is carried out, while in the control municipalities cannabis is sold under the existing tolerance policy. Comparing the two groups allows researchers to measure the impact of the regulated market against the illegal market.

Aims of the research

The primary goal of the experiment is to test the feasibility of a closed cannabis supply chain in which cannabis is legally produced by designated growers and supplied to coffeeshops. The results should provide insight into:

• The effects on public health, such as a reduction in health risks through the absence of pesticides or moulds in regulated cannabis products.
• The impact on crime and nuisance, in particular the reduction of illegal trade and nuisance through a regulated supply of cannabis to coffeeshops.
• The viability of an economic model for growers, distributors and coffeeshops in which quality and pricing remain competitive with the illegal market.

Central research question

The central research question is: What are the effects of a closed cannabis supply chain on public health, crime and safety? The aim is to evaluate whether regulated cultivation and sale can replace the illegal market, what its social effects are, and whether the new market offers advantages over the current tolerance policy.

Research methods

For the pre-measurement, data was collected through several techniques, including:

• Interviews with 130 stakeholders, including municipal departments, police, the public prosecutor and coffeeshop owners.
• Visits to 142 coffeeshops, counting 1,252 visitors and surveying 922 of them.
• Analysis of coffeeshop menus and surveys of nearby residents and coffeeshop staff.

Participating (intervention) municipalities

• Almere
• Arnhem
• Breda
• Groningen
• Heerlen
• Hellevoetsluis
• Maastricht
• Nijmegen
• Tilburg
• Zaanstad

Control municipalities

• Enschede (compared with Almere)
• Helmond (compared with Heerlen)
• Leeuwarden (compared with Groningen)
• Leiden (compared with Nijmegen)
• Lelystad (compared with Zaanstad)
• Roermond (compared with Maastricht)
• Tiel (compared with Arnhem)
• Utrecht (compared with Breda)
• Zutphen (compared with Hellevoetsluis)

Why are these municipalities paired?

The pairing between participating and control municipalities was made carefully on the basis of several comparative criteria:

• Size of the municipality: pairs are matched in scale to produce representative data.

• Number of coffeeshops: the number of coffeeshops is aligned between groups to give an equivalent picture of the market.

• Socio-demographic characteristics: municipalities with similar population structures, employment figures and social conditions are paired to make the comparison as accurate as possible.

• Geography: in some cases controls are chosen to capture regional effects, such as in border municipalities.

This pairing ensures that differences in outcomes between participating and control municipalities can be attributed to the experiment rather than to other variables.

Expectations

The success of the experiment depends on several factors, including the quality and diversity of regulated cannabis, pricing relative to the illegal market, and the enforcement of the closed chain by bodies such as the Inspectorate for Justice and Security (IJenV) and the NVWA. Whether regulated cannabis can compete with the illegal market is essential to achieving the goals of the experiment.

Research during the experimental phase

During the experimental phase, when only regulated cannabis may be sold in participating municipalities, the research will examine further:

• The extent to which the regulated chain meets users' expectations.
• The shift of consumers from the illegal to the regulated market.
• Enforcement and compliance behaviour of coffeeshops.
• The effectiveness of Track & Trace systems in maintaining a closed chain.
• Long-term effects on crime and public health, including the use of pesticide-free cannabis.

The experimental phase will deliver crucial insights into how a closed chain works, the viability of the model, and the impact on society. The research team continues to monitor on an ongoing basis, providing interim reports and informing policymakers about possible adjustments.

More information

For detailed information on the design and results of the research, see the full report: Summary of the WODC study (PDF).