The Dangers of Cannabis

New Zealand Centre for Political Research

The New Zealand Centre for Political Research is a web-based think tank that takes a research-based approach to public policy matters and encourages the free and open debate of political issues.

Last week in Parliament the Health (Protection) Amendment Bill passed its first reading and was referred to the Health Select Committee. The bill contained a section banning sunbed use for young people under the age of 18. Such sunbed age restrictions have already been adopted in other jurisdictions such as South Australia, the United Kingdom, Germany and California.

The Minister of Health, Dr Jonathan Coleman explained to the House that artificial UV tanning is associated with an increased risk of developing skin cancer and that younger people are more vulnerable: “There is strong evidence that people who use sunbeds increase their risk of malignant melanoma and other more common skin cancers. The greater the exposure, the greater the risk of skin cancer.”

The Minister went on to say, “The Government considers that the evidence of health harm gives sufficient justification for intervention, particularly in respect of controls to protect young people from exposure to sunbeds.”

What was clear from the debate was that Members of Parliament were unanimous in their desire to protect young people from what they considered to be a serious health risk. The Green Party in particular has been very outspoken on this issue for some years, calling not only for tighter regulations, but for an all out ban.

The Greens are also opposed to cigarette smoking because of the health risk, promoting the goal of a “Smoke Free Aotearoa” by 2025.

So while on one hand, the Greens want to ban such things as sunbeds and tobacco products because of the health risk, on the other hand they want to liberalise cannabis laws – even though the risk of cancer from smoking cannabis is far greater than from smoking cigarettes!

This week’s NZCPR Guest Commentator is the Director of the Medical Research Institute of New Zealand, Professor Richard Beasley, a physician at the Capital & Coast District Health Board, and a Professor at the Universities of Otago, Canterbury, and Southampton in the UK. I asked Professor Beasley, an expert in respiratory medicine, to outline for readers the dangers of smoking cannabis, especially to young people.

In his paper Cannabis and the Lung, he presents key observations from New Zealand studies of the respiratory effects of cannabis use. These include:

  • Significant respiratory symptoms and impaired lung function occur in cannabis-dependent individuals by the age of 21 years, even though the cannabis smoking history is of a relatively short duration.
  • One cannabis joint is equivalent to between 2.5 and 5 tobacco cigarettes for adverse effects on lung function.
  • Long term cannabis smoking increases the risk of lung cancer in young adults. The magnitude of the risk can be viewed in different ways:
    for each joint-year of cannabis smoking the risk of lung cancer increases by 8% (where one joint-year is equivalent to smoking one joint per day for one year, or one joint per week for 7 years, or the equivalent).
    the population attributable risk of lung cancer with cannabis smoking in young adults is about 5%, i.e. cannabis smoking causes one in every 20 cases of lung cancer in young adults.
  • One cannabis joint is similar to 20 tobacco cigarettes in terms of lung cancer risk. 

As Professor Beasley explains, smoking cannabis is far more harmful to human health than smoking tobacco cigarettes. In terms of cancer risk, smoking one cannabis joint is the equivalent of smoking 20 cigarettes, and in terms of the risk of lung disease, smoking one cannabis joint is the equivalent of smoking up to 5 cigarettes.

On their own, these are damning statistics, but when combined with other risks to health and safety it is easy to see why so many societies around the world have attempted to discourage all access to this drug.

Research conducted over a 20 year period by Professor Wayne Hall, a leading expert in addiction at King’s College in London and an adviser to the World Health Organisation, also links cannabis use to a wide range of harmful side-effects, from mental illness to lower academic attainment to impaired driving ability. These include:

  • One in six teenagers who regularly smoke cannabis become dependent on it, as are one in ten regular adult users
  • Cannabis can be as addictive as heroin or alcohol and can lead to hard drug use
  • People who smoke cannabis daily as teenagers are more likely to use other illicit drugs
  • Cannabis doubles the risk of psychosis and schizophrenia
  • Driving after smoking cannabis doubles the risk of a car crash, with the risk heightened yet further if they have had an alcoholic drink

Cannabis is clearly a very dangerous drug, especially for young people. It causes cancer, lung disease, psychosis, and can lead to the onset of schizophrenia. It is highly addictive and can become a gateway to hard drugs. In addition it causes impairment that can result in accidents, hospitalisation, or death.

The euphoria and other affects sought by cannabis users is primarily produced by delta-9-tetrahydrocannabinol (THC), which is highest in the flowering tops of the female cannabis plant. During the past 30 years the THC content of cannabis has been increased through selective plant breeding. In the US for example it has increased from less than 2 percent to an average of 8.5 percent by 2008. This means that the impairment caused by smoking cannabis is now far greater than it used to be. In addition, THC, which is stored in the fatty tissue in the body, can have a long term affect, since it can remain in the system for up to a month.

While supporters of more liberal cannabis laws often say that smoking the drug is a victimless crime, the facts show the opposite.

report from the New Zealand Transport Agency explains that two thirds of cannabis users admit driving under the influence, with cannabis impairment nearly doubling the driver crash risk even when alcohol is not a factor.

The statistics show that almost half of all drivers killed on New Zealand roads had alcohol, other drugs, or both in their systems when they crashed. One in five of these drivers had used cannabis only, over a quarter had used a combination of alcohol and cannabis, and another quarter had some other combination of drugs in their systems, possibly also including cannabis.

Three-quarters of the cannabis drivers who died caused the crash that killed them – and when alcohol and cannabis were mixed together nine out of ten dead drivers were responsible for the crash that killed them.

Of course it isn’t just road accidents that can be attributed to cannabis use. One only has to recall the dreadful 2012 Carterton tragedy, where 11 people lost their lives after their hot air balloon hit power lines, caught fire, and crashed to the ground to realise the devastating impact of cannabis use. In the final report of the Transport Accident Investigation Commission it was determined that the accident occurred as a result of pilot error – and cannabis impairment. The pilot had THC in his system and had been seen smoking cannabis shortly before the flight.

The potential danger of drug use in the workplace has been recognised through the Health and Safety in Employment Act 1992. This legislation places a duty on employers to provide a safe workplace free from hazards – including worker impairment due to drugs. As a result, employees working in safety sensitive areas are likely to be subjected to drug-testing.

In fact, because the potentially dire consequence of cannabis and other drug impairment in the workplace is now widely understood, a whole new drug testing industry has become established.

Air New Zealand set the legal precedent in 2004, successfully defending its drug testing policy against a six-union High Court challenge. The forestry industry followed in 2008, requiring a drug and alcohol-free workplace backed by drug-testing. Drug testing now covers 40 to 50 per cent of the workforce – including many in the training sector.

The fact that so many workplaces now require their employees to be drug free has also resulted in drug testing for the unemployed. Work-tested beneficiaries who are receiving welfare may be required to pass a drug test – if one is required by a potential employer – or risk losing their benefit.

Previously, the Labour Government allowed unemployed beneficiaries to refuse to apply for drug-tested jobs – if they knew they wouldn’t pass the test – without any consequences at all. But National’s welfare reforms changed the system to ensure that recreational drug use is no longer an acceptable excuse for avoiding work. With thousands of New Zealanders working in jobs that require them to be drug-free, and with around 40 percent of the jobs listed with Work and Income requiring drug tests, it is reasonable to expect work tested beneficiaries to be drug free as well.

Given the significant health and safety risks associated with cannabis use, why don’t our health officials and community leaders speak out more strongly about the dangers of this drug? Is their silence the reason that New Zealand has one of the highest reported rates of cannabis use in the world, with about three-quarters of the population having tried cannabis by the age of 25?

Why don’t the public service advertising campaigns that highlight the risk of lung cancer from smoking cigarettes warn young people of the dangers outlined by Professor Beasley, that smoking a single cannabis joint is equivalent to smoking 20 tobacco cigarettes in terms of lung cancer risk?

Why don’t political parties advocate for a more proactive approach in communicating the dangers of this drug to the New Zealand public – and especially to young people?

And what about the Greens? In the sunbed debate, Health spokesman Kevin Hague made the point that users were not given sufficient information about the risks: “the information that is available to them is insufficient for them to form a reasonable view and make an informed decision about the level of risk that they are incurring”. Isn’t it the same for the users of cannabis?

Judging by their track record of wanting to ban almost anything that appears to be causing harm, shouldn’t the Greens be leading the push for more public information and tighter laws – or are they so selfish in their political ambition that they are turning a blind eye to the perils of cannabis use lest they lose the support of the cannabis-using voting block?


Would you like to see the dangers of smoking cannabis promoted more widely?

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  • Seriously?? What a load of selective information you are presenting here. I have read a University of Sydney study on the effects of smoking pot and driving. The results were that pot smokers were safer than sober drivers but you will never read that in anything the establishment puts out. Really Get Frank, I thought you guys were independent and showed a balanced view. I am obviously wrong and you are in fact puppets to a higher master. Disappointed.

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