Herbal Remedy or Devil's Lettuce



Unless you have been living under a rock recently, you cannot but have noticed that there is a lot of political debate about whether cannabis should be legalised, decriminalised or made available on prescription. 

As ever there is a vast amount of misinformation in the media and online so we thought to try to provide some perspective.  Be warned - you may be surprised and may not like what we have to say here but it is as far as can be told, the truth.

Updated 19/07/19

So what is cannabis and how does it work?

The cannabis plant originated in central Asia, possibly the Himalayan region.  It grows well in temperate to tropical environments and so has found a place throughout the world.  It has been used in various forms for fibre (hemp), oil, medicine and as a recreational drug for at least 4000 years although it's spread into the Western world did not occur until the 16th Century.  Modern horticultural techniques have produced a wide variety of strains which thrive in most environments and have much higher yields.

Currently interest is focussed on cannabinoids, which are produced naturally by cannabis.  There are at least 85 different cannabinoids, of which Tetrahydridocannabinol (THC) and Cannabidiol (CBD) are the majority and most interesting.  THC is the psychoactive drug that results in the high from cannabis use, whilst CBD is not noticeably psychoactive.  The amount of CBD or THC produced by plants depends on the cultivar.  Recent selective breeding has produced plants that produce vastly more THC or CBD than would occur naturally although it is really the ratio of these products that changes as the total amount of cannabinoids is fairly constant; and as THC levels rise, CBD levels fall.  This is why the cannabis sold today is far more potent than what was available in the 1960s when it's recreational use became increasingly popular.  There is the same amount of total cannabinoids, just more of it is the psychoactive THC.

There is still a lot we don't know about the cannabinoid receptor system, what it does, what it is for and how stimulating the receptors has the effects it does.  THC acts by stimulating two specific proteins in the brain - the unimaginatively named CB1 and CB2 receptors.  These were discovered long before the naturally occuring compound which the body produces to activate them which was not discovered until 1990.  CBD actually blocks these receptors though it may cause them to increase in number with time.  It is vitally important to understand that whatever the endocannabinoid system's purpose and name, it is NOT to allow plant cannabinoids to have their effects - that is co-incidental.  The receptors were discovered because of research into how cannabis has its effects and named accordingly and have not evolved to allow us to take advantage of cannabis.

CB1 receptors seem to be involved in appetite and reward.  It is stimulation of these receptors that results in "the munchies" which are a common feature of recreational cannabis use.  These same receptors are also implicated in memory and may be relevant in the ability to 'get over' traumatic life events.  Interestingly, activation of the CB1 receptor with CBD has shown some potential in certain rare cases of intractable epilepsy but this effect is not improved by the addition of THC.  Blocking the receptors completely causes substantial apetite reduction but has a high risk of triggering depression and suicidal behaviour.

CB1 and 2 receptors also switch off peripheral nerves.  These seem to be responsible for the pain relieving effects of cannabis and stimulation of these in animal studies has been shown to reduce the response to controlled painful stimuli.

The number and proportion of CB1 and CB2 receptors seem to vary significantly from person to person which may account for the very variable effects of cannabinoids from person to person.

Medical Uses of Cannabis

Cannabis has been proposed as a potential treatment for nausea, multiple sclerosis, cachexia (a state in which the body does not use food properly), epilepsy and pain. 

There is little doubt that cannabis is an effective appetite stimulant for some people but the research data are at best equivocal when used as a medicine.  It might or might not improve cachexia in cancer.  There is some evidence of benefit in HIV related cachexia where small amounts of weight loss can be quite significant.

THC is a weak antiemetic, reducing nausea slightly.  It has been tested and found to be less effective than other more readily available medications.

CBD has been trialled in epilepsy but the studies have been small and weakly powered.  The only benefit found has been in the very rare Dravet Syndrome and that in one small study. Since original publication of this article, two further studies have shown possible benefit of CBD in treatment-resistant epilepsy.  The american FDA has approved it for use, but it is important to note that that does not mean it is effective and it is certainly not a sensible first choice treatment.  The studies were poorly performed and of low value so more research is needed to determine if CBD is effective as more than a placebo (epilepsy is, counterer-intuitively, very placebo-responsive)  The FDA approval reflects the relatively low risk of CBD and the lack of alternatives and should not be seen as an endorsement of medical cannabis use.

THC has been found to be effective in several studies of acute pain and the effect seems to be dose related.  In most studies significant benefit was found when smoking three high-potency doses daily.  Lower doses do not seem to be effective and at the doses required to be effective for pain, psychoactive effects are prominent.  Higher doses may also cause hyperalgiesia, actually increasing the perception of pain.  Despite the widespread use of medicinal cannabis in the USA and Canada for headache, there have been no studies to date investigating this.  The overall picture in chronic pain is that THC and CBD are no more effective than placebo and side effects of THC outweigh any benefit.

In Multiple Sclerosis, CBD is generally favoured over THC.  Both have been trialled and efforts are being undertaken to try to determine whether or not the ratio of THC to CBD is relevant in terms of therapeutic effect.  Several studies have investigated THC and whole cannabis extracts with some evidence of benefit in some patients.  These do tend to be small benefits and are of doubtful clinical significance overall, but a few patients do seem to benefit substantially whilst the majority gain little or no effect.

Cannabis has also been proposed for cancer treatment directly, with hemp oil being applied to skin cancers in an effort to cure them - this has not been found to be effective.

Cannabis is also popular in terminal care.  Some patients claim that it alleviates their symptoms and prefer it to other means of doing so.  There is no quality evidence one way or the other.  This is a thorny issue and comes to the side effects of treatment.  In our opinion, when we are talking about dying patients, the alleviation of symptoms is what matters and how that is done should as far as it is possible be up to the patient.  It is not as if the longer term consequences need to be considered after all.  Side effects are generally more prominent with cannabis than with opiates and users by and large have little insight into this.

Many users of cannabis find that it helps them to get to sleep.  It is highly valued for this purpose and occasional use will often make users sleepy.  This has not been subjected to formal clinical trial however so it is not possible to determine whether this has long term effects or not.

There are many other proposed uses and some practitioners prescribe cannabis products for multiple different conditions but none appear to have any basis in fact or have never been formally investigated.  It is not appropriate to consider treatments that have not been the subject of clinical trials.

Recreational Use

Cannabis is valued for several psychoactive effects - relaxation, euphoria and a tendency to think philosophically are the primary effects that are sought.  About 13% of people in New Zealand admit to regular use of cannabis and about 15% of them are heavy regular users.  This is approximately the ninth highest cannabis use rate in the world.

THC is effective whether taken orally or smoked, the effects taking from 30 minutes to an hour to develop after oral dosing and 30 seconds to 3 minutes after smoking.  About twice as much THC can be absorbed from the inhaled route as the oral route and the absorption is much more controllable and reliable when smoked. 

After absorption THC is taken up by body fat from where it is later released slowly.  This is compounded by reabsorption from the gut, where much of the drug is excreted.  It can take up to 30 days for a single dose to be excreted fully though the effects of such a dose are very small.

Users get very variable effects.  A proportion of people find that cannabis makes them paranoid, some find it makes them useless, others feel it makes them more productive.

We have included some patient stories which have been provided by regular users of cannabis, linked in the further reading section below.

Side Effects

THC has numerous side effects including unwanted weight gain, sleepiness, inattention, reduced motor skills, paranoia, psychosis, depression, suicidal behaviour and injury.

As has already been noted, stimulating CB1 receptors increases appetite.  Many cannabis users gain weight and this is dose-related.  Daily users gain more weight than weekly users.  Smoking cigarettes seems to counter this effect somewhat but comes with its own set of risks.

Sleepiness is a common problem with cannabis, especially soon after use.  This may persist for a prolonged period of time in some users, giving them characteristically part-closed eyes most of the time.  This is however a very variable effect and is only normally seen amongst frequent users, usually those who use cannabis daily.

Inattention and poor motor skills are a real problem.  It is very difficult to overdose on inhaled cannabis (though deaths do occur from excessive oral use) but users are at high risk of death from accidents.  This is a particular issue when it comes to workplace safety and driving with numerous studies proving conclusively that driving or operating machinery when under the influence of cannabis increases the risk of injury. 

Cannabis impairs judgement, making it difficult for users to see how impaired they are until after a considerable period without it.  This is accentuated by the slow wash-out with heavy users taking on average 1-2 weeks to notice improvements.  This also contributes to poor motivation and lack of productivity.

Up to 3% of users will develop significant paranoia and even lose a grip on reality briefly.  The reason for this is not clear but cannabis seems to exacerbate many mental illnesses whilst also helping to reduce the perception of many of the symptoms for users.  Cannabis use is also heavily corellated with suicide although it is likely that this is mostly due to the underlying problem not being treated effectively. 

Cannabis is addictive.   There is evidence of all aspects of addiction in some users including increasing use, desire to seek the drug and withdrawal symptoms when deprived.  These are generally mild however and withdrawal is never directly fatal.  Addiction is generally easier to overcome than alcohol and tobacco use, though this is in part due to the restricted availability.

Most medical uses of THC require it to be inhaled.  If smoked, there is a high risk of smoking related harm.  Studies in pain use for instance require three times daily smoking, which is associated in cigarette smokers which a 10 fold increase in lung cancer rates.

Perhaps the greatest harm from cannabis is the least known - it is used to mask and treat symptoms of mental illness.  Users often find that cannabis is effective to help sleep and reduce anxiety but whilst it reduces the symptoms, it does nothing to treat any underlying cause, resulting in protracted delays in seeking treatment.  This often means that by the time a user has made changes and got treamtent for their disorder and is feeling better they are 5-10 years older than other people at the same stage in their career.

There is evidence that cannabis legalisation in Colorado has reduced alcohol sales (by 13%) though there is no data on alcohol related harm.  Alcohol related road deaths have not reduced.  It seems likely that such a significant reduction in alcohol use will show benefits but that is not definite.  It is of course possible that those choosing not to purchase alcohol are the low-risk users in any case.  It is worth noting that some studies have shown an increase in alcohol sales, though we consider the reduction evidence to be more credible.

CBD use is not generally associated with significant effects.  There is good quality evidence that it is safe to use and significant harm has not been reported.

Legal Situation

Currently the posession of any quantity of cannabis is illegal under the Misuse of Drugs Act.  There are continuing campaigns to have this altered.

For medicinal use, medical grade cannabis-derived products (but not cannabis itself) containing THC can be imported with Ministry of Health approval for named patients with specialist authorisation.  Products which contain CBD can be purchased by general practitioners and on-sold to patients without any particular restriction.  These products are all sensitive to temperature so require storage in a refrigerator and are very expensive.  A month's supply costs about $500 as there is no subsidy.

In some parts of the world, most notably Colorado, which has similar societal mores to New Zealand, cannabis is legal for recreational and medicinal use.   Holland has long tolerated the sale of small quantities of cannabis and Portugal has decriminalised all drug use.  These will be discussed in the Way Forward section later.

Driving and Cannabis

Driving and cannabis has been a contentious issue. 

There are multiple studies showing that cannabis consumption impairs judgement and motor skills.

There are observational studies that demonstrate an increased probability of fatal and non-fatal accidents when driving after the consumption of cannabis.

A high proportion of drivers who test positive for cannabis in roadside tests, do so at levels consistent with recent use.

The evidence is overwhelming that cannabis use is not compatible with safe driving.

The contention arises because of the ability of THC to accumulate in fatty tissue.  Regular smokers can test positive for cannabis for up to four months after ceasing use completely and this provides the basis for the argument that they are not being impaired, simply 'washing out'.   THC also affects people variably so some will be clearly impaired whereas others will not at any given level.  Regular users may be functional at higher levels than occasional users.

These arguments are not dissimilar to the arguments against restricting alcohol when driving.  Alcohol does not have quite such a long wash-out period, but we know that there is an increased risk of crashes if driving the morning after the night before, even though most people who are over the legal limit would not feel intoxicated in such circumstances.

Cannabis also impairs judgement as to fitness to perform tasks so people tend to believe they are more capable than they are.

Religious Considerations

Many religions have prohibitions against intoxicating substance use, including Mormons,  Isalm and Buddhists.  Rastafari are reknowned for their use of cannabis as part of their culture although they are a small and relatively young group (founded in 1930s)  Most religions are indifferent to cannabis use, though some fundamentalist Christian and Muslim groups have campaigned actively to maintain prohibition.  The scriptural basis for this is unclear.

Gangs and Cannabis

Currently the major suppliers of cananbis in New Zealand are the various gangs.

Local production and importation result in large sales of the product though profits are low and it is not a big earner for gangs.  It is sold as part of the service to customers rather than as a major

Cannabis is not known to be a significant gateway drug (except to nicotine use) so the argument that gangs use the opportunity to push other substances is not well evidenced.

Most interaction between purchasers and suppliers of cannabis is through door-to-door sales and courier deliveries.  Visits to 'tinny houses' are much less common.

Whilst it is often believed that legalisation of cannabis would reduce gang influences, evidence does not support this.  In Colorado, illegal growing has increased by over 75% and organised crime cannabis related prosecutions have tripled since legalisation.  Overall a legal, regulated market increases drug related harm as compared with prohibition.  This was the case in the USA alcohol prohibition period where alcohol use fell to 30% of pre-prohibition use eventually rising to 70% towards the end of prohibition. 

Youth use in Colorado has not increased since legalisation.  It is important to note that prior to legalisation Colorado had unusually high youth use, which had been falling steadily

Income From Taxing Cannabis

Taxing sales of Cannabis products can lead to substantial income for authorities.

In Colorado, the revenue from legal marijuana sales is approximately USD 168 million annually (01/2014-01/2018) or around 228 million New Zealand Dollars per year.  Scaled for population (Colorado has 1 million more people) this would equate to perhaps $188 millon per year in NZ all other things being equal.

$168 million equates to about 0.01% of the NZ health budget in 2017.


The Way Forward

Ultimately New Zealand faces a choice.  Do we continue as we are, or do we make changes?  The options are as muddy as the debate unfortunately so it is difficult to discuss them clearly however, they broadly fall into these categories which do blend into each other somewhat:

  • Full legalisation.  Permit any use, growing and sale by anybody to anybody.
  • Restricted legalisation.  Permit any use, growing and sale by people meeting appropriate criteria
  • Restricted market.  Permit any use by people meeting appropriate criteria but restrict the production and sale (this is the Colorado approach)
  • Selected market.  Permit certain uses by some people meeting appropriate criteria.  General sale is not permitted (this is the current NZ approach)
  • Decriminalisation.  Sale and growing remains illegal but people are not charged if they are in posession of small amounts (this is how NZ police generally enforce the law and is the law in Portugal)
  • Prohibition.  All use remains illegal.

There are of course pros and cons of each approach.

Prohibtion, contrary to common belief, does not increase criminal behaviour.  Cannabis does not induce great cravings on withdrawal - the main withdrawal effect is insomnia - so people generally do not commit crime to obtain cannabis.  A heavy cannabis habit is currently cheaper than an average tobacco habit so cost is not an issue either.  It is important to consider the prohibition era in the United States.  The violence associated with alcohol prohibition was actually quite limited and had far more to do with the development of new organised criminal structures than prohibition itself.  After the ending of prohibition, organised crime in the united states continued to increase finally peaking between about 1975 and 1995, after which it has begun to decline.

Unfortunately prohibition does lead to the criminalisation of people who are doing no-one else any harm.  With the exception of their tendency to be involved in accidents, users of cannabis tend not to cause harm to others.  As discussed above, they are generally not criminals in other respects but can spend considerable amounts of time being punished for posession of relatively small amounts of the drug.  Currently posession carries up to three months in prison or a $500 fine (a considerable amount to a beneficiary equating to about 3 month's disposable income at the time of writing)  There is a considerable body of opinion (but little evidence either way) that this is counterproductive and causes more harm than good.

Portugal has developed a novel approach, keeping all drugs illegal but choosing not to prosecute people caught with less than 10 day's supply of them.  If caught, offenders are required to appear before a tribunal which will discuss their needs and offer support.  Repeat offenders do get prosecuted.  This has been credited with a substantial reduction in the Portugese drug use problem which is now down to levels only slightly worse than in New Zealand.  This latter point is important - although drug use has declined in Portugal since this law was brought in, they still remain higher users than in New Zealand.  Nevertheless, the reduction in harm has been significant and the burden on the legal system has been reduced.

The appeal of the restricted market is that it allows regulated use and taxation of cannabis.  It is possible to restrict use to people more likely to be responsible with the drug and of course to obtain a modest amount of taxation income from it.  It is unlikely that this would result in a significant reduction in court costs however as currently posession of the amounts permitted in Colorado is not penalised in NZ either.  Any taxation income has to be balanced against an increase in benefit payments to those unable to work as a result of cannabis use, whether directly or as a result of accidents.  There is also a significant moral question to be asked when using taxation income as justification for legalisation.  Is it morally appropriate for the government to gain financially from selling a product that is known to be harmful, and where such markets are proven to increase use?

Restricted markets also generally offer a less desirable product than black market cannabis - it is usually lower potency and as such does act as a gateway drug.  Users try the legal option then find that better weed is cheaper from the gangs.  This has the effect of increasing gang incomes and influence whilst reducing their risks of production and sale.

A selected market, allowing sales under specified conditions avoids the issues around the societal cost of cannabis use, restricting use to those who can demonstrate they would benefit (or at least come to no harm) from cannabis use.  Permitting the use of cannabis in terminal care or HIV cachexia would be good examples of this.  Such people are seldom well enough to be participating fully in society and have a limited life expectancy in any case.  It would also permit wider medical research of greater quality to be undertaken.

Full legalisation of course comes with all the benefits except taxation, however once it is legal for anyone to grow their own it becomes effectively impossible to control in any way.   It is in practical terms impossible to regulate the amount or strain of cannabis being grown so any legislation permitting people to grow cannabis is effectively full legalisation without restriction.

Summary and Opinion

There are some clear facts which arise from consideration of cannabis in society:

  • Cannabis has some limited medical applications
  • Evidence for medical use is very weak
  • Where evidence for medical use exists, benefits are generally small.
  • Most claims for medical benefit of cannabis have no supporting evidence at all.
  • For all medical uses of cannabis, more effective alternatives exist.
  • Legalisation of cannabis has been shown to increase use and to increase cannabis related driving accidents in a society structurally similar to New Zealand.
  • Criminal penalties for cannabis tend to result in greater harm than cannabis itself.
  • Cannabis legalisation may reduce alcohol sales.  There is no evidence that this reduces alcohol-related harm.
  • Cannabis itself is harmful to users.  Any benefits must be considered in the context of this harm.
  • Smoking of any substance increases the risk of lung cancer dramatically.
  • CBD is not a high-risk substance, though benefits are minimal.

What if any changes should be made to New Zealand law in order in the light of media pressure on the subject of cannabis?

Our opinion, based on a thorough review of the facts is that the current situation in New Zealand probably reflects the best evidence to date and that significant further relaxation of the law is more likely to do harm than good.

We would support a very limited extension to the use of cannabis in medicine, including funding of CBD based products under special authority (patients must meet criteria that suggest they are likely to benefit from treatment) and permission for those with HIV cachexia or any condition likely to be fatal within 6 months to use cannabis in any way they choose. 

We do not support other medical uses, including the use of THC in chronic pain as there is no evidence to support benefit being any greater than current treatments, whilst the side-effects are generally greater.

We are concerned that greater decriminalisation of cannabis will result in an increase in the risk of fatal and non-fatal vehicle accidents and workplace injuries.  This is supported by strong evidence from Colorado where the rate of cannabis related road deaths has more than doubled since it was decriminalised.

We do not support suggestions that income from the sale of cannabis is a valid justification for a controlled market.  This is immoral as it implies that profit is an acceptable reason to supply a substance with significant known harms and in any case is offset by the increased costs of managing the market, increased benefit payments, and reduced productivity resulting from increased use.

We support a gentle approach to the handling of users caught with small quantities of cannabis for personal use.  Prosecution of such users benefits no-one.

Perhaps the best argument in favour of cannabis reform is that as it is so readily available now, everyone who will be harmed by it is already being harmed by it.  This is in fact quite valid, though the Colorado experience suggests that use does increase post legalisation, particulary amongst younger people.  It also works against legalisation as it suggests that there is also no actual need to increase access. 

It is particularly important to note that the Colorado experience is of sudden change.  Young people turning 18 this year have had 5 years to get used to the idea of cannabis being available legally.  How they respond to the experience will be far more relevant than looking at the last 5 years.

CBD, although relatively ineffective is also very safe.  There is no reason for CBD to be considered to be the same as THC in law.

We recommend that other than legalisation of CBD, there should be no significant changes to cannabis law, but that as new evidence may come to light that it would be appropriate to review this in 5 years. 


We welcome correspondence about this article through our Facebook page.  Please do not use the website contact form to get in touch as responses will not be given that way.

We realise that this article will not please everyone.  It is however as close as it is possible to get to a dry, factual assessment of the state of cannabis in New Zealand today, the evidence around medicinal uses and the conclusions can be supported by the findings here. 

If you think you have good evidence that we may have missed, please link to it from our facebook page.  We will be pleased to respond that way.


Medical Marijuana Sign Nita Lind


Additional Reading

Getting High on the Endocannabinoid System

Marijuana and AIDS

Cannabis Oil Not Wise for Skin Cancer

Patient Experiences of Cannabis Use


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