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


UKCIA is a cannabis law reform site dedicated to ending the prohibition of cannabis. As an illegal drug, cannabis is not a controlled substance - it varies greatly in strength and purity, it's sold by unaccountable people from unknown venues with no over sight by the authorities. There is no recourse to the law for users and the most vulnerable are therefore placed at the greatest risk. There can be no measures such as age limits on sales and no way to properly monitor or study the trade, let alone introduce proper regulation. Cannabis must be legalised, as an illegal substance it is very dangerous to the users and society at large.

5 thoughts on “A summary of the health harms of drugs (NHS) – Critique of the cannabis information

  1. How is cannabis being related to tobacco? There two different things.. Nicotine kills 430,000 people per year.. while Marijuana has zero deaths per year.. Nicotine causes cancer… Marijuana helps that cancer. Nicotine should be the drug and pot should be the safe thing to smoke instead. but yet we have it ass backwards, bc America is ass-backwards still.. We have the drugs thats aren’t as bad for you as illegal and the drugs( nicotine,Alcohol, pharmaceuticals) that are bad for the body are legal. come on America, use your head and not your ass, your making us all look stupid.

  2. As ever, Derek, you are right in denouncing the hypocrisy of our drug laws and of those who support them, implicitly or explicitly — especially of politicians, policy makers and lobbyists who should know better. I wonder what the world would be like if alcohol and tobacco were illegal and their production and consumption were considered a criminal activity. Oh, wait! We already know. It would be like today…only worse! No matter the drug, just say NO to Prohibition and the War on Drugs!

    Gart Valenc

  3. Madness, true madness anyone?.
    “To do the same thing over and over again,
    and to expect a different result”. No?
    Propaganda. Its actualy getting a little painful to read and watch such utter armchair science ruling the day. Reading things like this. Any child can understand logic if explained to them. My 9 year old daughter undertands life more than those in power. Shame on them a thousand times for protecting the alcohol and tobbacco industry’s. History will i Hope show them all up for they are. The Banks went bust we pay the bill. We want freedom we pay with our Freedom. Sickening. Enough already Banning anything creats false demand it appeals too the youth but sure they know this already. a sign of a healhty society is one which has a prison population. Time we puled these wall’s down and wake up collectivly. Enough.
    Thanks again Derek for sheding the light.

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