3.32 Health effects of smoking other substances

This section is not intended to provide a comprehensive overview of drug use other than tobacco, but to highlight that the deliberate inhalation of smoke from the combustion of any matter is potentially injurious to health. The health effects of smoking any substance will depend on various factors, including the age at which smoking commences, the duration for which the body is exposed to the smoke, and the concentration and nature of constituents of the material smoked.

The scientific literature describing the health effects of smoking tobacco is comprehensive but the same cannot generally be said of other smoked substances, particularly where use is illegal. For example, in the case of marijuana, its illegality has militated against broad-based population studies, although data gathering has improved with its growing public acceptance (see Chapter 1, Section 1.10). Lack of adequate funding for medical and epidemiological research is a factor in some countries where smoking of substances other than tobacco may be more widespread. Another reason that these other forms of smoking have been under-researched is that the relatively small numbers of users and the scattered pattern of their geographical distribution make systematic study more challenging. Despite these issues the evidence base is sufficient to allow important conclusions on the adverse health effects of smoking these other substances on their own or in various combinations with tobacco. Here we cover the findings with regard to the smoking of herbal and other non-tobacco cigarettes and cannabis.

3.32.1 Herbal and other non-tobacco cigarettes

Herbal and other non-tobacco cigarettes may erroneously be considered as a safer alternative to smoking, or an aid to quitting smoking, and are actively promoted as such by some manufacturers.¹ Cigarettes combining herbs and tobacco have been produced in China since 1959, and they are now manufactured in South Korea, Taiwan and Thailand.² These cigarettes are commonly promoted with messages implying that they are aids in quitting, are less harmful than conventional cigarettes, or with claims for active health benefits such as raising immunity or protecting the kidneys.

Cigarettes that do not contain tobacco or nicotine may still produce toxic substances including carcinogens. A 2015 study assessing the safety of mainstream smoke from herbal cigarettes, compared with a generic tobacco cigarette, concluded that some harmful components—specifically, tar, carbon monoxide, benzo(α)pyrene, and phenolic compounds including hydroquinone, resorcinol and catechol—exist in the mainstream smoke of herbal cigarettes in large amounts similar to a tobacco cigarette.³ Although tobacco-specific components such as nicotine and nitrosamines were not detected, the study showed smoke condensates of herbal cigarettes have mutagenic potential similar to that of tobacco cigarettes arising from combustion of the product.³

Research has examined the DNA damage response arising from exposure of human lung cells to smoke from tobacco- and nicotine-free cigarettes (made from lettuce and herbal extracts). This exposure led to formation of double-strand DNA breaks that are potentially carcinogenic; there was a dose–response relationship between exposure to the smoke and the severity of ensuing DNA damage response. The study concluded that smoking tobacco and nicotine-free cigarettes is at least as hazardous as smoking cigarettes containing tobacco and nicotine.⁴

A 2009 study conducted in China tested the claim by the tobacco industry in that country that herbal cigarettes are less harmful than regular cigarettes. Four discriminating biomarkers were analysed from urine samples provided by 135 herbal cigarette smokers and 143 regular smokers. Importantly, the researchers found a concern about their health to be one of the main reasons that smokers switched from regular to herbal cigarettes and they reported increased consumption after doing so. The researchers found no significant difference in the levels of the four biomarkers between smokers of herbal cigarettes and smokers of regular cigarettes, concluding that herbal cigarettes did not deliver less carcinogens than regular cigarettes and that the Chinese tobacco industry should avoid misleading the public by promoting herbal cigarettes as safer products.⁵

An analysis of ‘vegetable-based cigarettes’ manufactured in France and sold in Austria were found to yield levels of carbon monoxide at least as high as those produced by conventional cigarettes. Analysis of other constituents of the smoke was not made, although initial studies had shown that combustion may have produced carcinogens and other noxious chemicals.⁶ Investigations of ‘non-nicotine, non-tar’ herbal cigarettes popular in the Philippines has also shown significant yields of tar and carbon monoxide.⁷ Smokers attempting to use herbal cigarettes as an adjunct to quitting are therefore exposing themselves to dangerous tar and carbon monoxide levels, without actually increasing their chance of quitting.

3.32.2 Cannabis (marijuana, hash, ganja)

The main forms of cannabis are marijuana, hashish and hashish oil. Marijuana comprises the dried leaves, flowering tops and stems of the hemp plant Cannabis sativa. The more concentrated resin from the flowers is called hashish. Cannabis is usually smoked as a cigarette (joint), through a pipe or water pipe (bong).⁸ Cannabis contains molecules called cannabinoids that affect the brain and some other organs. There are over 60 different types of cannabinoids present, with the most common one being THC (tetrahydrocannabinol), which binds to receptors in the brain.⁹ Studies have reported the emergence of synthetic cannabinoids; these compounds are more potent than traditional cannabis and have been widely used to deliver products with psychoactive properties while circumventing drug legislation. As a result, authorities around the world are now beginning to exert control by either naming individual compounds or using generic legislation.¹⁰ Some early research indicates that synthetic forms of cannabis may be more likely to provoke psychosis in vulnerable individuals.¹¹

Cannabis is an illegal drug frequently used by Australians. Data from the National Drug Strategy Household Survey (NDSHS) 2019 indicated that 11.6%—about 2.4 million Australians—had used cannabis in the last 12 months, up from 10.4% in 2016. In addition, 36%—roughly 7.6 million Australians—had used cannabis in their lifetime, up from 35% in 2016. Among people who had used cannabis, 37% stated they used it weekly or more, with the predominant methods of use being in a joint (83%) or through a bong or pipe (72%). The use of cannabis within the last 12 months has increased among older Australians. Statistically significant increases when compared to 2016 data were recorded for recent cannabis use among persons aged 50-59 years (9.2%) and persons aged over 60 (2.9%). Among recent cannabis users aged 14 years and over, 29.3% identified as daily tobacco smokers, a statistically significant decrease from 34.3% in 2016. Among people aged 14 years and over who had recently used cannabis, 35.3% identified as never tobacco smokers, and 22.1% as ex tobacco smokers.¹² Continued use of cannabis may lead to both physical and behavioural addiction, especially among regular, heavy users, and those who start using the substance at an earlier age.¹³

In 2017, the National Academies of Sciences, Engineering, and Medicine published a comprehensive evidence-based report titled The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research.¹⁴ Broad categories of the health effects of cannabis smoking explored in the report included cancer; cardiometabolic risk; respiratory disease; immunity; injury and death; prenatal, perinatal, and postnatal exposure to cannabis; psychosocial; mental health; problem cannabis use and cannabis use and abuse of other substances. The report categorised the reviewed scientific evidence into conclusive, substantial, moderate, limited and no, or insufficient, evidence to support an association. The following findings are summarised in this order.

There were no findings from current scientific research that could be classified as conclusive evidence.

Substantial evidence of a statistical association was found for:

• long-term cannabis smoking and respiratory symptoms including cough, phlegm, and wheeze, as well as more frequent chronic bronchitis episodes
• maternal cannabis smoking and lower birth weight of the offspring
• cannabis smoking and the development of schizophrenia or other psychoses, with the highest risk among the most frequent users
• cannabis smoking and increased risk of motor vehicle crashes

Moderate evidence of a statistical association was found for:

• regular cannabis smoking and increased symptoms of mania and hypomania in individuals diagnosed with bipolar disorders
• cannabis smoking and a small increased risk for the development of depressive disorders
• cannabis smoking and increased incidence of suicidal ideation and suicide attempts with a higher incidence among heavier users
• cannabis smoking and an increased incidence of suicide completion
• regular cannabis smoking and an increased incidence of social anxiety disorder
• acute cannabis smoking and impairment in the cognitive domains of learning, memory, and attention
• an increased risk of unintentional cannabis overdose injuries among children, including respiratory depression or failure, tachycardia and other cardiovascular symptoms, and temporary coma. Note: these findings were only found in US states where cannabis use is legal
• cannabis smoking and the development of substance dependence and/or a substance abuse disorder for substances, including alcohol, tobacco, and other illicit drugs.

Limited evidence of a statistical association was found for:

• current, frequent, or chronic cannabis smoking and non-seminoma-type testicular germ cell tumours
• cannabis smoking and the triggering of acute myocardial infarction; increased risk of ischemic stroke or subarachnoid haemorrhage
• occasional cannabis smoking and an increased risk of developing chronic obstructive pulmonary disease (COPD) when controlled for tobacco use
• maternal cannabis smoking and pregnancy complications for the mother; admission of the infant to the neonatal intensive care unit (NICU)
• cannabis smoking and an increase in positive symptoms of schizophrenia (e.g. hallucinations); likelihood of developing bipolar disorder, particularly among regular or daily users; development of any type of anxiety disorder, except social anxiety disorder; increased symptoms of anxiety (near daily cannabis use); increased severity of post-traumatic stress disorder symptoms among individuals the disorder
• cannabis smoking and impaired academic achievement and education outcomes; increased rates of unemployment and/or low income; impaired social functioning or engagement in developmentally appropriate social roles.

No, or insufficient, evidence was found to support an association between cannabis smoking and:

• incidence of oesophageal cancer; prostate cancer, cervical cancer, malignant gliomas, non-Hodgkin lymphoma, penile cancer, anal cancer, Kaposi’s sarcoma, or bladder cancer, risk of developing acute myeloid leukemia/acute non-lymphoblastic leukemia, acute lymphoblastic leukemia, rhabdomyosarcoma, astrocytoma, or neuroblastoma in offspring (parental cannabis use)
• an increased risk of acute myocardial infarction
• hospital admissions for COPD, asthma development or asthma exacerbation
• other adverse immune cell responses in healthy individuals; adverse effects on immune status in individuals with HIV; Increased incidence of oral human papilloma virus (HPV)
• all-cause mortality; occupational accidents or injuries; death due to cannabis overdose
• later outcomes in the offspring (e.g. sudden infant death syndrome, cognition/academic achievement, and later substance use)
• changes in the course or symptoms of depressive disorders; the development of post-traumatic stress disorder.

In 2020, a systematic review of systematic reviews examining cannabis use and related health harms was conducted.¹⁵ As well as confirming the above findings from The National Academies of Science’s 2017 report,¹⁴ the 2020 review¹⁵ also added evidence of an association between cannabis smoking and:

• cardiovascular risk (ischemic strokes, hyper-tension and thromboangiitis obliterans),
• cognitive attainment (fewer years of education, lower education attainment, concentration alteration and detrimental effects on everyday cognition
• injury implications (violence perpetration, homicide victims, crash responsibility and crash involvement)
• prenatal exposure (cognitive dysfunction and behavioural disturbances).

Relevant news and research

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References

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15. Campeny E, Lopez-Pelayo H, Nutt D, Blithikioti C, Oliveras C, et al. The blind men and the elephant: Systematic review of systematic reviews of cannabis use related health harms. European Neuropsychopharmacology, 2020; 33:1-35. Available from: https://www.ncbi.nlm.nih.gov/pubmed/32165103