26 Aug A summary of the health harms of drugs (NHS) – Critique of the cannabis information

Cannabis has never killed anyone directly.

That is a claim which has been made for years now by the cannabis law reform campaigns and has always been treated with some derision by those who insist cannabis is a prohibited drug because it’s dangerous. Well, now we can not only say it but we can actually provide a reference from, of all places, the British Government.

‘A summary of the health harms of drugs’ (here) is published by the Department of Health (not the Home Office which usually dishes out the less than factual information concerning drugs). The NHS issued a press release which describes the publication (here):

“An updated guide summarising the health harms of drug and alcohol misuse is available, aimed at supporting non-medical practitioners working with substance misuse issues.

A summary of the health harms of drugs” updates the 2003 “Dangerousness of Drugs” guide, outlining acute and chronic problems associated with each substance, as well as:
* Factors that mediate or moderate the risk
* Potential health risks linked to substances commonly added to illicit drugs
* The influence of different circumstances of use, e.g poly-substance abuse
This essential guide for drug and alcohol treatment professionals provides the most up to date scientific evidence on the health harms arising from licit and illicit substance misuse.”

And just in case you were wondering makes clear that

“It is not connected to the work of the Centre for Crime and Justice Studies, the Independent Scientific Committee on Drugs, or Professor David Nutt.”

Nothing personal, you understand.

Interestingly it recognises something which the Home Office drugs unit has always been reluctant to accept

“In particular, the harms associated with illicit substance use, or use of other unregulated psychoactive substances, are further confounded by lack of suitable quality control in their manufacture and distribution. People who use these substances can therefore only make inadequate assessments of the quality, purity, and chemical composition of any drugs they use”

This come close to accepting that government policy in the shape of prohibition is creating an extra level of harms, but doesn’t quite manage to say so. It addresses the thorny issue of how to talk about prohibited and approved drugs by using the terms “licit” and illicit”, which it defines as

“Licit drug – A drug that is legally available with or without a medical prescription

Illicit drug – A psychoactive substance, the production, sale, possession or use of which is prohibited”

The first and perhaps most important thing to notice about this publication is it gives similar types of information about drugs “licit” or illicit”. It is therefore easy to make comparisons between the effects of prohibited drugs like cannabis and the legally available alcohol and tobacco; in other words a drug “controlled” (sic) under the misuse of drugs act and those not. It makes for interesting reading.

In terms of the Acute adverse effects associated with the use of cannabis it states

“••no cases of fatal overdose have been reported
••no confirmed cases of human deaths”

Which confirms the claim that cannabis has never directly killed anyone

The other acute adverse effects associated with the use of cannabis listed really relate to the symptoms of intoxication in the main, things like “difficulty in motor co-ordination”, or methods of use such as irritant effects of smoke on the respiratory system (coughing, sore throat and bronchospasm among people with asthma).

Next it lists the “Chronic adverse effects associated with the use of cannabis”

••no conclusive evidence that cannabis causes cancer”

That is very different from the claims made on the Talk to Frank which told us

“Cannabis, like tobacco, has lots of chemical ‘nasties’, which can cause lung disease and possibly cancer with long-term or heavy use”

But of course Frank is a product of the Home Office drugs unit.

Acute adverse effects associated with the use of cannabis also include

“••cannabis use may be an important risk factor for the development of respiratory cancers but the relationship is unclear*
Chronic respiratory disease*
••chronic bronchitis
••lung damage
••number of reports in the literature of an association between cannabis use and bullous lung disease in relatively young users”

But with the following important caveat:

*Studies of the harms associated with cannabis use are limited by confounding as many users smoke tobacco as well as cannabis, or use tobacco as vehicle for smoking cannabis resin. Although tobacco smoke and cannabis smoke are known to contain a similar range of mutagens and carcinogens, actual exposure to these compounds may differ between tobacco and cannabis users in terms of the frequency and duration of use, and because of factors such as the depth of inhalation”

There is also the fact that THC seems to retard cancer growth which isn’t mentioned. So the main acute effects of using cannabis is not causing cancer and being mixed up with tobacco use. This goes right to the heart of the Toke pure safer use campaign and the need to separate the use of cannabis and tobacco, proof if ever we needed any.

It is a little odd that the list of acute effects of using cannabis should contain something it doesn’t do, but not causing cancer isn’t the only acute non-effect listed, apparently

“evidence for the effects of cannabis on human immune function is limited”


“no evidence of structural change in brains of heavy long term cannabis users”


“no severe or grossly debilitating impairment in cognitive function”


“tolerance to psychoactive and physical effects unlikely to occur unless there is sustained heavy exposure”

not to mention

inconsistent and mixed evidence for whether heavy, chronic cannabis use is associated with a persistent ‘amotivational syndrome’ characterised by social withdrawal and apathy”

In other words no real evidence, but we thought we’d mention it anyway. Now of course these are all claims made against cannabis over the years so perhaps it’s right to debunk the myths, but listing these things as “Acute adverse effects associated with the use of cannabis” is strange, when they’re not.

It does list some apparent acute adverse effects associated with the use of cannabis however

“like tobacco, cannabis use in pregnancy may be harmful to foetal development; studies show a consistent association between cannabis use in pregnancy and reduced birth weight – though less so than as a result of tobacco smoking during pregnancy”

Although there are lots of studies which do not show this effect, hence the “may be harmful”. Does that count therefore as an “acute effect”?

“some reports that children born to women who have used cannabis in pregnancy may face mild developmental problems; however, the evidence is mixed and confounded by the other situational, health and lifestyle factors and polysubstance use in this population e.g. cannabis users are more likely to use tobacco, alcohol and other illicit drugs during pregnancy”

So again, the evidence for this is at best weak.

“use can inhibit reproductive functions and disrupt ovulation, sperm production and sperm function”

Although cannabis users can and do still have babies, so the effect can’t be that acute.

“persistent sore throat”

Well, maybe but it’s not a common condition that I’ve ever been aware of.

Perhaps the most revealing section is that concerning the psychological/psychiatric of cannabis:

“evidence that early initiation and regular, heavy cannabis use is associated with a small but significantly increased risk of psychotic symptoms and disorders in later life”

Which is a good argument for an age limit on sales, which of course is impossible under prohibition.

“complex association between cannabis use and schizophrenia – some evidence that use may exacerbate psychotic symptoms and is linked with relapse but it is unknown whether this is a universal risk or due to differences in individual vulnerability”

That’s a fair comment and a long way from the simplistic reefer madness claims of a few years ago.

“insomnia, depression, aggression, anxiety”

This claim will come as a complete surprise to many, given cannabis’s reputation for inducing placid behaviour in users. Aggression is not a feature of cannabis use many would recognise, neither is lack of sleep. The links between cannabis and depression can also be challenged, with some evidence that cannabis can alleviate the condition (see this study) and anxiety is usually – if at all – related to intoxication.

It claims

“good evidence for a cannabis dependence syndrome
•frequent, heavy users are at the greatest risk of dependence”

Which is not rocket science really, although after listing some symptoms of withdrawal it does state

“••some evidence of a withdrawal syndrome among heavy users”

So presumably most do not suffer withdrawal?

Lastly we have the “Factors that mediate and moderate harms associated with the use of cannabis”.

In routes of administration (why do they have to use such sterile language for methods of use?) it lists without comment


No reference to the many different ways to smoke is made, or the options of smoking without tobacco

“oral consumption – makes dosage difficult to regulate and unpleasant reactions more difficult to avoid”

An effect of the legal regime of course. “Oral consumption” – in English eating or drinking – of course avoids any dangers connected with smoking.

“overall benefits and harms of the use of alternative delivery systems for inhalation, such as through vaporisation, have not been well studied”

Which does raise the question of why they haven’t?

Under “Dose” it says

“health effects of increases in the potency of cannabis products are not clear; may depend on the impact on routine use, however there is evidence of binge use among some users increasing the risk of dependence and psychotic symptoms”

Again, no mention of different strains and the increased harm caused by not knowing the nature (strain) of the cannabis consumed – caused by government policy.

It lists as a concurrent use

“Smoking with tobacco”

It lists some of the social context and setting of cannabis use, including “perceived” medical uses and the possibility of self medication by psychiatric patients. It also states

“widely used by opiate and crack cocaine users”

Which may be true, but it hardly a surprise. it also acepted that cannabis is

“sole illicit drug used by a proportion of the population”

Under developmental issues, another non-effect is noted

“suggestion that regular use may encourage users to progress to other forms of drug abuse; the likelihood of this occurring is more related to the lifestyle and personality of the individual and access to sources of other illicit drugs than the effect of cannabis itself”

So cannabis does not lead on to other drugs, the “gateway theory” so beloved of prohibition supporters.

Individual vulnerabilities are listed as

“••increased risk of experiencing psychotic symptoms in vulnerable individuals e.g. those with a personal or family history of schizophrenia
••use may precipitate relapse of schizophrenia
••use may adversely affect the course of schizophrenia”

Which means the risk is restricted to people at risk of suffering from, or already suffering from, mental illness. Confirming what we have already learned and demolishing the claims of the reefer madness scare. Finally it lists

“stimulating effects on the cardiovascular system of the major psychoactive compound in cannabis (THC) can be detrimental to individuals with cardiovascular or respiratory disease”

Now all this looks like quite a lot, but it isn’t really – especially as a great proportion of the acute and chronic effects are actually things cannabis doesn’t do. Frankly if these non-effects were not listed, it would be a pretty short check-list indeed. Of course, all these listed effects take no account of the fact that cannabis comes in many different forms or strains of plant, with greatly differing ratios of the important chemicals THC/CBD. So all these acute and chronic effects are made much worse by this uncertainty caused by government policy.

Legal situation

“Misuse of Drugs Act 1971
Class B
cannabis, cannabis resin”

All this is thrown into sharp focus when we look at the tobacco section. Chronic adverse effects associated with the use of tobacco:

“• Cardiovascular disease
• coronary heart disease
• peripheral vascular disease
• blood clots may form in the arteries supplying the heart (coronary thrombosis) or the brain (cerebral thrombosis) leading to a heart attack or stroke
• lung
• digestive tract (mouth, tongue, throat and oesophagus)
Respiratory disease
• chronic obstructive pulmonary disease, defined by a long-term cough with mucus (chronic bronchitis) and/or destruction of the lungs over time (emphysema)
• death from slow and progressive breathlessness

Exposure to second hand smoke
• coronary heart disease and lung cancer among adults

Cancers strongly linked to smoking
• cancer of lung, mouth, pharynx, larynx
• cancer of oesophagus, bladder, kidney, pancreas
• cancer of stomach, liver, cervix, nose, lip

Association with mental health disorders
• strong association between mental health disorders, including schizophrenia and mood disorders, and tobacco smoking
Significant risk factor for dementia
• Alzheimer’s disease
• other types of dementias
• evidence of cognitive decline among elderly smokers”

And of course, it’s highly addictive. There is much more there if you’re interested, but that’s enough to make the point because under “legal situation” it says

“Not controlled under Misuse of Drugs Act 1971”

Which just shows the rank hypocrisy of our present drug laws. The health impacts of tobacco far outweigh those of cannabis, yet cannabis is subjected to prohibition and its users are regarded as criminals. Tobacco is not included in the Misuse of Drugs Act because politicians decided it shouldn’t be, for no other reason. At the heart of this of course is the mistaken idea that the Misuse of Drugs Act is a prohibition act, which it isn’t. If it were enacted properly it could control drugs by a range of means and could easily cover both cannabis and tobacco. But politicians see things in simplistic black and white and pay more attention to the rantings of the Daily Mail than to objective science, the result is this mess.

But as regards the NHS pamphlet, it’s not bad. Although the inclusion of acute and chronic effect that cannabis doesn’t do in the way it’s been done is odd, at least it debunks the myths and provides evidence to counter the claims of ill informed media reports and politicians.

A special thanks to Jake Ish of CLEAR for help in creating this critique