Heart and lungs

Cannabis lung health risks underestimated

“One third of people think cannabis is harmless despite the fact that smoking it is 20 times more likely to cause cancer than tobacco,” The Daily Telegraph reported today. The Independent says that young cannabis users “do not realise the huge danger to their health”.

The stories are based on a new report, published by the British Lung Foundation, which says that public awareness of the health consequences of smoking cannabis is “worryingly low”, with almost one-third of the British population believing that smoking cannabis is not harmful to health. This figure rises to almost 40% among those aged under 35, the age group most likely to have smoked it, according to the survey. The report also highlights that many of the same cancer-causing compounds in cigarettes are also present in cannabis, and that the way cannabis is smoked may mean that the body retains more of these harmful products than when smoking a similar quantity of tobacco. One study has suggested that over the course of a year smoking a single joint each day could do the same lung damage as smoking 20 cigarettes per day over the same period.

The report calls for a public health education programme to raise awareness of the impact on the lungs of smoking cannabis and on its links to wider health problems, as well as more investment in research on the health consequences of using cannabis.

What did the report look at?

The report has been published by the British Lung Foundation (BLF). It reviews the current evidence on the impact of smoking cannabis on lung health and also on wider physical and mental health. It also includes the results of a survey it commissioned on public awareness of the health consequences of smoking cannabis.

Who uses cannabis?

The latest figures show that nearly one-third (30.7%) of people aged 16 to 59 in England and Wales have used cannabis in their lifetime, a figure which rises to 34.5% among 16-24 year olds. It’s estimated that about 2.2 million people aged 16 to 59 have used cannabis in the last year. This makes cannabis the most commonly used illicit drug in the UK. The report does not distinguish between different methods of using cannabis (e.g. eating foods containing it), but smoking the drug is generally acknowledged to be the most common method of use.

What type of cannabis do people smoke?

The report says that the type of cannabis people smoke has changed over the last decade, with increasing numbers smoking marijuana, also known as ‘herbal’ cannabis. This is made up of the plant’s dried leaves and female flower heads (the other type being hashish, which is made up of the secreted resin, leaves and flower heads compressed into blocks).

It seems that in recent years there has been a trend towards cannabis smokers using marijuana rather than hashish – in 2008, marijuana comprised 81% of all police cannabis seizures, compared to 30% in 2002.

Is it true that the cannabis available today is stronger than in the past?

The potency of cannabis is measured according to its concentration of a chemical called tetrahydrocannabinol (THC), the main component associated with its mood-altering effects.  The report says that in the UK the strength of herbal cannabis, as measured by the amount of THC it contains, almost doubled between 1995 and 2007 (from 5.8% to 10.4%). The report suggests this means that previous research on the effects of cannabis may not be applicable to current smokers.

What does cannabis smoke contain?

The report says that the constituents of cannabis smoke are similar to those of tobacco smoke apart from the presence of THC (which is only in cannabis) or nicotine (which is only in tobacco). This means that cannabis smoke has the same carcinogens (substances that cause cancer) as tobacco smoke, although concentrations of these may be up to 50% higher. Like tobacco, cannabis also contains toxic carbon monoxide.

It also points out that although people generally smoke cannabis less often than tobacco cigarettes, the way they inhale means the amount of smoke reaching the lungs is greater. The respiratory tract and the rest of the body may also retain far more of the products of cannabis smoke than when smoking a similar quantity of tobacco. Given the similarities in their constituents, there is concern that regularly smoking cannabis could have similar health risks as regular tobacco smoking, says the BLF.

Also, people often mix cannabis with tobacco. There is strong evidence that smoking tobacco causes lung cancer and chronic lung disease. This makes it difficult to isolate whether health problems are specifically caused by cannabis or tobacco, says the report.

What lung conditions is cannabis linked to?

The report says that although cannabis is the world’s most widely used illicit drug, there is surprisingly little research into its effects on lung health, with far less reseacrh into the effects of cannabis smoke than tobacco smoke. However, it says there is now research showing that the active component, THC, can suppress the immune system and that cannabis smokers may be at risk of:

  • respiratory problems such as chronic coughing, wheezing, sputum production, acute bronchitis, airway obstruction
  • infective lung conditions such as tuberculosis and Legionnaire’s disease
  • pneumothorax (collapsed lung)
  • lung cancer – one study, which was widely quoted in the papers, suggested that smoking just one cannabis cigarette a day for one year increases the risk of developing lung cancer by a similar amount to smoking 20 tobacco cigarettes for the same period. It concluded that 5% of lung cancers in those aged 55 or under may be caused by smoking cannabis.

However, the report points out that there is a lack of conclusive evidence as to the possible effect that smoking cannabis has on lung function and the risk of developing chronic obstructive pulmonary disease (COPD). There is evidence that smoking cannabis with tobacco leads to a greater risk of COPD than smoking tobacco alone.

What about other health conditions?

The report says the wider impacts of smoking cannabis are well-documented and may include dependence, increased risk of motor vehicle accidents, increased risk of cardiovascular disease and of mental health problems.

Can cannabis be used medicinally?

Some research suggests that cannabis may have legitimate medical uses including the treatment of chronic pain, the prevention of vomiting caused by cancer chemotherapy, and the relief of pain and diarrhoea in Crohn’s disease. However using 'crude cannabis' as a medicine is still not sanctioned because of its toxic components, says the report, and further work is needed to develop safe and effective cannabis-based medicines.

What else did the report find?

The BLF also commissioned a survey of a representative sample of 1,045 people across Britain to find out more about levels of public awareness of the health consequences of smoking cannabis.

The survey found that 88% believed that tobacco smoking poses a greater risk of lung cancer than smoking cannabis. However, one study has suggested that smoking just one cannabis cigarette every day for one year increases the risk of developing lung cancer by a similar amount to smoking 20 tobacco cigarettes for the same period, although further research is needed to confirm these findings and to identify the mechanisms by which cannabis smoking may cause lung cancer.

People were also asked to identify which activities from a list provided were harmful to health. While 88% identified smoking tobacco as harmful and 79% identified eating fatty foods, 68% identified smoking cannabis as harmful.

What does the BLF recommend?

The BLF suggests a public health campaign targeted at younger people on the potential health risks of smoking cannabis. It also recommends further investment in research to provide 'more conclusive' evidence on the effects of smoking cannabis on lung function, COPD and lung cancer.

NHS Attribution