Cannabis Research Review: What The Research Says About Cannabis Legislation

Authors: Luke McIntyre, Chia-Wei Jao, Ben Riorden

Currently, New Zealanders are voting on whether to legalise cannabis for recreational use. Specifically, the referendum asks New Zealanders to indicate whether they support “Cannabis Legalisation and Control Bill”, which aims to legalise cannabis while also introducing strategies to reduce harms (e.g., limit advertising, age limits). Understandably, given the current events around the world, this issue has been somewhat overshadowed. However, what is concerning is the lack of easy to read, evidence-based, and politically neutral information available. It is important that we are all able to access the research in a way we can understand, particularly for the key issues.

Whilst scientific data is helpful in making decisions it is important to note that there is still much to learn about cannabis in NZ and overseas. Cannabis has not been legalised overseas for long periods in most places, however, that should not stop us from looking at what the research is currently telling us. It is also important to note that comparisons are also difficult due to the variety of methods some places have legalised cannabis (e.g., heavily regulated vs. decriminalised).

In this article we aim to show everyday kiwis what the research says about cannabis legalisation in the hopes that all New Zealanders will be able to make an informed decision when they vote on this issue.

What is in the bill?

One common misconception is that New Zealanders are simply voting to legalise cannabis or not. What we are actually voting on is whether we support the “Cannabis Legalisation and Control Bill”, which outlines the way in which cannabis would be legalised.

The bill will allow government to control and regulate growing, selling, buying and consuming cannabis. Businesses selling cannabis would need to acquire a license and abide by the regulations. A person aged 20 or over could buy up to 14 grams of cannabis a day and grow 2 cannabis plants if they want. People under the age of 20 found in possession of cannabis would pay a fine. It would be illegal to consume cannabis in public, possess more than 14 grams in public, grow cannabis in public, or supply under 20-year olds.

Will legalisation lead to higher usage rates? Who will this affect the most?

This is one of the most discussed points in the general public when we talk about legalisation. So, what does the data tell us?

What we know is that around 80% of New Zealanders born in the 1970s have tried cannabis at least once in their life[1], with 70%-80% of people consuming it before the age of 25[2]. In fact, New Zealand has one of the highest Cannabis use rates, per capita, aside from North America and Micronesia[3]. Regarding increased usage rates people are most concerned about youth usage rates rather than older age groups. The research suggests that places that have high usage rates pre-legalization, such as NZ, do not see a large increase in young people using cannabis once it is legalized[4].

When Canada legalised cannabis there was a 2% increase, mainly in males and those over the age of 25[5]. Further, daily use has not increased in Canada, except for those over the age of 65[6]. In contrast, the data from the USA shows an overall 1%-5% increase, which was seen mostly by those in College (18+) or people over 25[7]. In fact, there have been either small increases, no increase and even evidence showing decreases in usage in the US, Canada and Uruguay, who have all legalised Marijuana in certain areas[8]. Importantly, the holistic data appears to show no significant change in usage rates for those under the age of 25[9].

When comparing the data from 2018/2019 to data from 2011/2012 we can see a usage increase of 15% in New Zealanders aged 15-24[10]. This means that currently 29% of this age group have used cannabis in the last year and the trend is on the up in the unregulated, illegal market[11]. If we were to legalize cannabis, the research from Colorado suggests that there would not be an increase in marijuana use for 15-18-year old’s[12]. In fact, research from Canada after legalization shows that use in the past three months has decreased by almost 50% for those aged 15-17[13]. This is expected to have occurred due to the age of purchase being set at age 18, cannabis being seen as ‘less cool’ when legal, and greater funding into education. With NZ setting the proposed age of purchase at 20 it could be expected that we would see similar results as Canada but extended to the 15-19 age group.

We are trying to improve mental health outcomes in NZ, what effect will legalisation have on this?

Mental health is an important part of our well-being and overall health. When making decisions like this we need to know how cannabis can affect aspects of our mental health such as anxiety, depression, and psychosis. The main research in this area focuses on psychosis as this is where the most common cannabis-related issues are. Studies show that cannabis users are more likely to experience psychotic symptoms and/or psychotic disorders, but only if the use of cannabis began during adolescence[14][15][16][17][18][19]. Further, this relationship was only found for those who possess a genetic vulnerability and began the use of cannabis during their early adolescent years[20].

Other mental illness research found a relationship between regular cannabis use and increased bipolar disorder symptoms[21]. The main area of debate is whether cannabis causes this or whether those who are more likely to have bipolar disorder are simply more likely to try cannabis. There is weak evidence for a relationship between cannabis use and anxiety and depression, but again the direction of the relationship is unknown[22]. Essentially the question becomes: Are individuals who suffer from mental illness more likely to use cannabis, or does cannabis use cause mental illness? Some research shows an association between regular/heavy users of cannabis and depression, if use started young and continued into mid-adulthood[23]. Regular cannabis use and suicidal ideation, or suicide attempts, has some link for users aged 14-15 years old but not those at age 20-21 years. This emphasises a pattern of risk declining with increasing age[24], which would suggest that legalisation would be a safer option for youth than the current system.

An area that may be of more concern is Cannabis Use Disorder (CUD), which is the continued use of cannabis despite clinically significant impairment and physical dependence. Importantly, studies found that trying cannabis did not always lead to further use, and further use did not lead to the development of CUD in most cases[25]. A meta-analysis found that only people who reported daily, or near daily, use of cannabis in the past year, developed CUD. This risk increases if cannabis use is begun early[26]. CUD is not something we want to see increasing, currently research shows that without policies and regulations we can expect increases in cannabis use and CUD among those most vulnerable[27]. Through implementing policies and regulations, we can help prevent CUD and protect those most vulnerable.

Interestingly, there also appears to be various benefits of cannabis for mental health, such as posttraumatic stress disorder, with 19% of cannabis users reporting use to manage PTSD[28]. This use was found to improve sleep and coping with the negative symptoms of PTSD[29]. Research of cannabis and PTSD is still in its early stages and these results need to be taken with caution.

Overall, the research shows that higher potency cannabis is associated with some mental health problems. However, it also shows that there is more risk for individuals with genetic predispositions and adolescents. The proposed cannabis policy would take steps toward reducing adolescent use and putting a cap on potency which currently is not in place in the illegal market. It is important to note that there still needs to be more research to fully learn the potential benefits of cannabis.

Is Cannabis a ‘gateway drug’?

A topic that is frequently discussed in these debates is whether cannabis is a gateway drug. Whilst there is certainly some correlation between cannabis use and other drug use it is not the cannabis itself that appears to cause any correlation. When looking at any biochemical link, animal studies of cannabis use in both adults and adolescents[30] did not lead to the increased use of other drugs[31], except for nicotine[32]. Essentially, although there is research that shows that individuals who use cannabis regularly are more likely to engage in illicit drug use[33], cannabis itself does not appear to be the cause. Frequently engaging with drug dealers, the behaviours of the social group, and getting into the drug market at an ‘entry level’ through purchasing cannabis illegally are more likely to lead to the consumption of ‘harder’ drugs[34] [35].

Data from four states in the USA, where cannabis has been legalised, shows that opioid use does not increase[36], cocaine us does not increase[37], and tobacco rates have continued to fall[38]. Further, the majority of cannabis users do not go on to use other ‘harder’ drugs[39].

Cannabis can’t be good for you, can it? What are the physical health outcomes?

Cannabis users have shown to have worse physical outcomes such as respiratory problems [40], gum disease, cardiovascular disease, and diabetes. However - when compared to cannabis users - tobacco users had worse lung function, systemic inflammation, and metabolic health at age 38 years. Cannabis users were not found to have other physical health problems in early midlife[41]. Importantly, in the United States, there was no increase of youth treatment admissions after the recreational marijuana legalisation in Colorado and Washington[42].

We know the negative consequences for those who smoke tobacco, but while cannabis smoke has shown to impair respiratory function; it has not been associated with various cancers[43].

Specifically, research has found that there does not appear to be a relationship between cannabis smoking and lung or colorectal cancer[44][45]. Interestingly, cannabis has been shown to kill various cancer types[46] [47]. When looking at the specific compounds in cannabis, it was found that cannabis smoke releases a protective effect, whereas nicotine smoke increases a carcinogenic effect (cancer causing)[48]. Research has shown that cannabis can cause some harm to brain health, however, these harms were shown to recover with a long period of abstinence[49]. Currently there is promising research suggesting that cannabis could relieve neuropathic pain and chronic pain[50], although this research is ongoing.

Similar to mental health there are some limitations in the current research on cannabis and physical health. Whilst potential benefits would help many individuals, and potential negatives could cause health issues, more research is needed.

Won’t cannabis make us stupid?

There is concern that cannabis use will affect IQ, particularly how this would affect education for younger individuals. The Dunedin study found that the amount of cannabis use was important in whether there was any impairment. They found that as cannabis dependence increased, mean IQ scores decreased (up to 6 IQ points) even when taking into account other substance dependence and education. However, impairment and larger IQ decline was mainly seen among those who started using cannabis during adolescence and used it frequently. This study also showed that stopping cannabis use fully restored neuropsychological function among those individuals, if use began in adulthood but not adolescence[51].

Interestingly, when the researchers took into account the users environment, how much cannabis they used, their IQ at age 15 and how well they performed at school at age 16, they found that there was no difference in IQ or academic performance for those who had used cannabis 50+ times, compared to those who had never used cannabis[52]. A study that compared different sets of twins found that twins who were cannabis users did not show a bigger decline in IQ compared to their twin, when controlling for genetic factors. This suggests that cannabis users with lower IQs already had low IQ scores before cannabis usage and that the decline in IQ was not due to cannabis usage[53].

The general research highlights that there are many other factors that contribute to decline in IQ and educational performance, however, there is still the potential vulnerability in adolescent onset-users, emphasising the importance of prevention among adolescents.

Won’t legalizing cannabis lead to more motor vehicle accidents?

There is a general concern that legalising cannabis will lead to more motor vehicle accidents, particularly in regard to fatalities. In a country where alcohol related deaths are a serious issue, will cannabis have a similar effect?

The research from overseas is mixed as to whether fatalities increase but those that have shown increases have generally only seen relatively small increases[54]. This is dose-related, meaning that the more cannabis consumed the more likely to be involved in a motor vehicle fatality. The most robust studies have been conducted in Colorado and Washington and have shown that fatalities did not significantly increase post-legalisation[55]. One study comparing these states showed an increase in Colorado (1.46 deaths per 1 billion vehicle miles traveled per year) but not in Washington[56]. On average any increases from studies in the US have lasted no more than a year and averaged 1.1 fatalities per million people, following legalisation[57]. In NZ this would average around 5.5 deaths in the first year after legalisation. Interestingly some studies have shown an 8%-11% decrease in traffic fatality post-medicinal cannabis legalisation, with a 13%-15% decrease in alcohol related fatalities[58].

It is important to take caution when interpreting these studies as often drivers weren’t tested in regard to how impaired they were at the time of the accident, only that they had cannabis in their blood. Further, who was at fault for the accident wasn’t always taken into account. It is therefore conceivable that the true rate of cannabis caused fatalities is even lower than the data suggests. More research is needed to confidently determine these outcomes.

Summary

Overall, for these main issues, the research suggests that: 

1) Usage rates will not dramatically increase. Increases will be seen mainly in the over 25 age group and there will likely be lower usage by those under the age of 18. 

2) It is still generally unclear whether cannabis actually causes more mental health issues, with the exception of psychosis. It could be that those who are more likely to suffer mental health issues are also more likely to try cannabis. 

3) Although there is evidence linking cannabis use to other drug use this is generally due to it being an illegal activity where individuals are more likely to come in contact with other drugs. Research that shows that the actual substance itself leads people to further drug use is generally weak. 

4) It is well known that cannabis can cause negative health outcomes, however, there is clear evidence to show that tobacco is associated with far worse health outcomes. Further, there is some evidence to show that cannabis use may actually have some positive health outcomes. 

5) The main research that has focused on cannabis use and IQ has shown that, when taking other factors into account, cannabis does not cause a long-term loss of IQ unless frequent use began in adolescence. 

6) Although there may be an increase in traffic accidents post-legalisation this increase will likely be very small, particularly in relation to fatalities. As driving while under the influence would be illegal there would likely be more testing done for this than there currently is.

Whether you decide to vote ‘yes’ or choose ‘no’ we hope that this article has been helpful in presenting the research from New Zealand and abroad to provide a clearer idea of the main issues surrounding cannabis legalisation.

For more information, research, opinions and more feel free to visit the references provided.

[1] Patterns of recreational cannabis use in Aotearoa New Zealand and their consequences: evidence to inform voters in the 2020 referendum

[2]Prevalence and correlates of cannabis use and dependence among young New Zealanders; The Christchurch health and development study: review of findings on child and adolescent mental health

[3] World Drug Report 2020

[4] Association of State Recreational Marijuana Laws with Adolescent Marijuana Use

[5] What has changed since cannabis was legalized?

[6] What has changed since cannabis was legalized?

[7] Changes in Marijuana Use across the 2012 Washington State Recreational Legalization: Is Retrospective Assessment of Use before Legalization More Accurate?

[8] Legalising cannabis in Aotearoa New Zealand: What does the evidence say?

[9] Has the Legalisation of Medical and Recreational Cannabis Use in the USA Affected the Prevalence of Cannabis Use and Cannabis Use Disorders?

[10] Legalising cannabis in Aotearoa New Zealand: What does the evidence say?

[11] Cannabis Use 2012/13: New Zealand Health Survey

[12] Association of State Recreational Marijuana Laws with Adolescent Marijuana Use

[13] Canada - what's been happening since legalisation?

[14] Association of cannabis use with adolescent psychotic symptoms.

[15] Association of combined patterns of tobacco and cannabis use in adolescence with psychotic experiences

[16] Cannabis use and risk of schizophrenia: a Mendelian randomization study

[17] The contribution of cannabis use to variation in the incidence of psychotic disorders across Europe (EU-GEI): a multicenter case-control study.

[18] Cannabis legalization: Did we make a mistake? Update 2019

[19] Cannabis use in adolescence and risk for adult psychosis: longitudinal prospective study

[20] Moderation of the Effect of Adolescent-Onset Cannabis Use on Adult Psychosis by a Functional Polymorphism in the Catechol-O-Methyltransferase Gene: Longitudinal Evidence of a Gene X Environment Interaction

[21]Tyler, Jones, Carter, Barrowclough (2015) The relationship between bipolar disorder and cannabis use in daily life: an experience sampling study.

[22]Gobbi, Aktin, Zytynski et al., 2019

[23] Lifecourse trajectories of cannabis use: a latent class analysis of a New Zealand birth cohort

[24] Cannabis use and suicidal ideation

[25] Palmer et al., 2009 Developmental epidemiology of drug use and abuse in adolescence and young adulthood: Evidence of generalized risk

[26] Leung et al., 2020 What is the prevalence and risk of cannabis use disorders among people who use cannabis? a systematic review and meta-analysis

[27] Budney et al., An update on cannabis use disorder with comment on the impact of policy...

[28] Bonn-Miller et al., 2014; Bohnert et al., 2014; Greer et al., 2014

[29] Bon-Miller et al., 2014

[30] Ellgren et al., 2007

[31] Solinas et al., 2004; Panlilio et al., 2007; Panlilio et al., 2013

[32] Panlilio et al., 2013

[33] Hall & Lynskey, 2005

[34] Fergusson et al., 2006

[35] Hall & Lynskey, 2005

[36] Centers for Disease Control and Prevention

[37] Substance Abuse and Mental Health Services Administration (SAMHSA)

[38] Substance Abuse and Mental Health Services Administration (SAMHSA)

[39] National Institute on Drug Abuse

[40] Hancox et al., 2015

[41] Meier et al., 2016 A Longitudinal Comparison of Persistent Cannabis vs Tobacco Users

[42] Mennis et al., 2020 Adolescent treatment admissions for marijuana following recreational legalization in Colorado and Washington

[43] Sidney et al., Marijuana use and mortality

[44] Hashibe et al., 2005 Epidemiologic review of marijuana use and cancer risk

[45] Tashkin 2005 Smoked marijuana as a cause of lung injury

[46] Munson et al., 1975

[47] Sanches et al., 2001

[48] Pirce et al., 2004 Metabolism of nicotine and induction...

[49] Yucel et al., 2016 Hippocampal harms, protection and recovery following regular cannabis use

[50] Nugent et al., 2017 The effects of cannabis among adults with chronic pain and... general harms

[51] Meier et al., 2012

[52] Mokrysz et al., 2016 Are IQ and educational outcomes in teenagers related to their cannabis use? A prospective cohort study

[53] Jackson et al., 2016 Impact of adolescent marijuana use on intelligence: Results from two longitudinal twin studies

[54] Legalising cannabis in Aotearoa New Zealand: What does the evidence say?

[55] Fatal crashes in the 5 years after recreational marijuana legalization in Colorado and Washington; Crash Fatality Rates After Recreational Marijuana Legalization in Washington and Colorado

[56] Association of Recreational Cannabis Laws in Colorado and Washington State with Changes in Traffic Fatalities, 2005-2017

[57] Cannabis legalization: Did we make a mistake? Update 2019

[58] Medical marijuana laws, traffic fatalities, and alcohol consumption

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