Study: Licensed cannabis farms may reduce illegal cultivation more than bans

A new study from the UC Berkeley Cannabis Research Center suggests that licensed cannabis farms may be a stronger tool against unlicensed cultivation than both local bans and traditional enforcement. The study examines developments in California between 2018 and 2024 and challenges the idea that stricter bans automatically lead to less illegal production.

Licenses showed a clearer effect than bans

Researchers analyzed both licensed and unlicensed cannabis cultivation in California after legalization. The material included satellite mapping, spatial modeling, policy reviews, interviews in several counties, and data from the regulated supply chain.

The clearest conclusion is that the presence of licensed farms in an area was the most consistent factor linked to reduced unlicensed production. Local cultivation bans did not show the same stable effect. According to the researchers, bans were not a strong or consistent indicator of whether unregulated cultivation increased or decreased.

Unregulated cultivation moved rather than disappeared

The study describes a rapid increase in unlicensed cultivation between 2018 and 2020, followed by a sharp decline through 2022. After that, levels stabilized at roughly where they had been in 2018. At the same time, researchers observed a clear shift from pure outdoor cultivation to mixed-light production, where greenhouses and controlled lighting are combined with natural growing conditions.

The researchers also highlight a so-called “whack-a-mole” effect. When bans and strict enforcement pushed growers out of one area, operations could move on to more remote locations. This risks pushing cultivation toward cheaper, harder-to-monitor and sometimes more environmentally sensitive land.

Civil oversight appears to work better over time

An important shift in the study is the difference between punishment-focused enforcement and civil regulation. The researchers found that civil tools, such as fines, landowner responsibility and environmental rules, became more effective over time. Traditional eradication-focused enforcement, however, had a declining effect, especially when the remaining unlicensed growers often had few other livelihood options.

This does not mean that regulation alone solves the problem. The study also points out that complicated licensing processes can prevent growers from entering the legal system. If the path to a license is too expensive or too complex, regulation risks creating a group of growers who remain outside the system even though they could have been brought into it.

California offers a broader lesson

For European policymakers, the conclusion is relevant but not directly transferable. California has a specific history involving legalization, local cultivation bans, extensive legacy cultivation and major geographic differences. Even so, the study shows an important principle: a functioning legal market can be a more effective competitive force against unregulated production than bans that merely shift the problem elsewhere.

The researchers therefore recommend that California maximize the number of licensed growers, create simpler pathways for smaller farms, make personal cultivation practically possible and improve the track-and-trace system. The broader idea is that cannabis should be integrated into normal agricultural and oversight systems, rather than treated as an exception with extreme penalties and special rules.

Sources

Licensed and Unlicensed Cultivation Across Ban and Permit Jurisdictions

Licensed farms are the strongest deterrent to unlicensed cannabis cultivation, UC Berkeley study finds