COMMENT:

New Zealand is debating its cannabis policy, a process that led to legalisation of cannabis use and supply in Canada just last month. Since the two countries share many traits and values - and high cannabis use rates - they have many insights to share on these matters.

In Canada, where cannabis reform had been discussed for decades, legalisation was advanced not principally to further the freedom to use drugs. Rather, the rationale included recognition that cannabis prohibition had done more harm than good, and that only through legalisation could cannabis be better controlled and regulated towards protecting public health and safety.

Based on my involvement in Canadian science and policy here is a - certainly incomplete and subjective - list of shared thoughts as New Zealand searches for its own path:

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• Beware of extreme ideological positions: The cannabis policy debate includes extreme claims that cannabis is merely an innocuous drug which, beyond, can miraculously heal many ills – while the counter position suggests that its use inevitably results in severe health harms.

Neither is correct; rather, the truth lies somewhere in the middle: Much of cannabis use results in no or little problems, although it bears risk for a variety of (physical and mental) health harms.

Serious harms occur predominantly with young, vulnerable or intensive users consuming high-risk cannabis products. Unfortunately, prohibition has been ineffective in curtailing these risks – but rather amplified many. As with all psychoactive substance use, good policy can at best strive for fear-reaching reductions of harms to public health.

• Develop consistent policy across substances: Much of the cannabis legalisation debate focuses on legal age of access. While many argue that use should not be allowed until the mid-20s due to alleged health (e.g., brain development) risks for younger users, there is no unequivocal evidence supporting such a cut off.

The higher the age restriction, the more young users will be excluded from the protective provisions of legalisation, and remain forced into illegality. Moreover, if youth protection was a consistent interest, New Zealand's legal alcohol age should immediately be elevated, given its equal – if not greater – health risks.

Best cannabis regulations will inevitably involve compromises, yet there are no evidence-based reasons to regulate cannabis more restrictively than alcohol. Most of the rest is up to good education and prevention efforts.

• Find good balance for key regulations: There are natural inclinations to pursue public health by restrictions, especially where uncertainties exist. In Canada, this has led to regulations in some provinces where legal cannabis purchasing is restricted to government stores and use to one's private home.

Such restrictions are not only practically unrealistic but likely to be counterproductive, since a quintessential challenge for feasible cannabis realities already exists: the vast, unregulated, illegal cannabis market.

Cannabis legalisation for public health will only succeed if providing reasonable provisions for users to leave illegal markets and behaviours. This requires appropriate arrangements concerning cannabis supply, access and use to be legally created.

•Separate medical and non-medical cannabis regimes: Many claims exist for cannabis' therapeutic benefits – some backed by evidence, many not. However, most current cannabis use occurs for non-medical – that is, recreational - purposes. For sincere policy reform this requires separate regulatory regimes with appropriately different standards for these two realms.

People with relevant health conditions should have reliable, medically-controlled access to high-quality medical cannabis therapy where supported by good evidence. Sensible cannabis policy, however, is not advanced by regimes where those desiring to smoke a joint for pleasure are conditioned to rationalise this as "therapeutic" behaviour, and doctors function as sanctioning gatekeepers.

• Keep the cannabis industry at bay: Cannabis is the new gold rush industry, with staggeringly lucrative business and profit prospects. Policy makers in North America have decided – and the same appears likely in New Zealand – that commercial producers supply legal cannabis markets.

In Canada, more than 120 commercial producers were already licensed on legalisation day, with many more coming. While the cannabis industry has advanced a popular discourse of providing a "healthy" product (compared to other legal substances), the simple truth applies here also that any commercial industry's overarching objective is to sell as much product as possible (especially when involving shareholders).

Such dynamics have resulted in extensive public health harms with alcohol and tobacco – and should not be repeated for a newly legal cannabis industry. Thus, government's need to establish – and staunchly defend - effective and comprehensive industry regulations.

Just as in Canada, effectively regulated legalisation of cannabis promises to be the superior approach for New Zealand towards improved public health and safety.

Legalisation, however, is no panacea and remains a policy experiment, until concrete impacts can be assessed. Since few actual case studies exist, and much depends on policy context, prospective outcomes will depend on many details.

As New Zealand and Canada are striving for similar goals concerning cannabis policy reform, they have many lessons and experienced to share.

Dr Benedikt Fischer holds the Hugh Green chair in addiction research at the University of Auckland. He acted as scientific advisor to the Canadian Federal Government in developing its cannabis legalisation framework.