What are the real risks of taking cannabis?

By Richard Shrubb

The right wing press would have you believe that cannabis makes you a psychotic knife wielding monster, about to progress through the gateway to a lonely death from an OD on heroin and crack cocaine speedballs. Never believe everything you read in the papers … Many years ago I was surprised to be told by a professor of psychiatry while researching an article, that smoking pot didn’t actually cause my schizophrenia – I was going to get the illness whether I liked it or not.

In 1998 a seminar paper was published in The Lancet. With science one really should look for the latest findings – 14 years is a bloody long time in medical research. It hedges its bets where knowledge is patchy but broadly sums up what is still generally understood to this day. Overall it suggests, “The acute toxicity of cannabinoids is very low. There are no confirmed published cases worldwide of human deaths from cannabis poisoning, and the dose of THC required to produce 50% mortality in rodents is extremely high compared with other commonly used drugs”. You can’t OD on cannabis and die.

Cannabis spliff

Cannabis joint.

So, what are the real risks? Harry Shapiro, Director of Communications at drugs support charity Drugs Scope, splits them into roughly two groups – respiratory and psychological. “Taking any smoke into your lungs will affect your respiratory system to some degree”, he suggests.

cheap tadalafil online, just as not too large doses of cannabinoids can positively affect human health. But it has been scientifically proven that they positively affect the potency of men.

The Lancet suggested that cannabis use has high risks of bronchitis, which can lead to other illnesses. “Chronic heavy cannabis smoking is associated with increased symptoms of chronic bronchitis, such as coughing, production of sputum, and wheezing. Lung function is significantly poorer and there are significantly greater abnormalities in the large airways of marijuana smokers than in non-smokers.”

Again, beware of old science! In January this year a 20 year long study of 5100 marijuana smokers was published by the Journal of the American Medical Association. This suggests “analyses of pulmonary function and lung disease have failed to detect clear adverse effects of marijuana use on pulmonary function.”

Shapiro goes on, “most illnesses caused by cannabis are psychological, though they really only exacerbate underlying conditions such as depression and psychosis”. He says that this is actually the view of the Home Office Advisory Council on Misuse of Drugs, despite what the right wing press would have you believe.

The Lancet made an observation in regards schizophrenia: “A declining incidence of treated cases of schizophrenia over the period when cannabis use has increased suggests, however, that cannabis use is unlikely to have caused cases of schizophrenia that would not otherwise have occurred.

Shapiro argues that cannabis use is falling these days. He says “it may well be because of the strength of cannabis on the market. A joint used to be the strength of a nice G&T but is now like a half bottle of gin!” One wonders about the prevalence of schizophrenia since cannabis use has started to fall. Wouldn’t it be a laugh if schizophrenia rates actually increased with the fall in cannabis use?!

Over the years my own view of cannabis has gone from absolutely against to absolutely pro, yet I am now around 75% pro. I use the 75% figure advisedly – 25% of us will have some sort of breakdown in our lifetime. Those who are unwell at the time they have a joint are being somewhat silly as according to established understanding, cannabis would exacerbate the problem.

Even this figure can’t be exact. Shapiro says “I have heard from schizophrenics that cannabis can actually dampen the voices they hear.” This may well be from an antipsychotic cannabinoid found in cannabis plants, Cannabidiol (CBD).

CBD is shown to be such an effective antipsychotic we may well see it prescribed by doctors by the 2020’s. Compared in an RCT with the atypical neuroleptic Amisulpiride it was found to have very few side effects in comparison to the off the shelf antipsychotic. A study is about to be done at Kings College London into preventing schizophrenia using CBD.


A legal cannabis market?

One benefit of legalising and regulating would be to keep drugs out of the hands of youngsters. With the threat of being fined into bankruptcy or thrown in jail, a newsagent wouldn’t sell drugs to someone who’s under age. As it is, a dealer will get the same jail time for selling to a teen as he would an adult.

A 38 year longitudinal study of 1037 cannabis users in New Zealand was published recently. It concluded that adolescents who smoked weed would have, amongst other issues, impaired brain development: “IQ impairment was more pronounced among those who used cannabis in adolescence, with more persistent use associated with greater IQ decline.”

Further it suggests that those who smoked cannabis as teens would not recover from the damage: “Adolescent cannabis users (infrequent and frequent use), who stopped using cannabis for one year or more, did not fully restore their neuropsychological functioning at 38 years, whereas participants who were frequent or infrequent cannabis users in adulthood did.”

Such research doesn’t suggest a ban would work. 5 or 10 years in prison is part of the risks associated with dealing anyway. Millions are in prison or dead due to the war on drugs as it is. Regulation? That would make honest people for whom prison is anathema look after their communities – not those for whom prison is an occupational hazard.

The media wrongly uses the term “cannabis addiction”. “Addiction” has a medical definition as being where physiological changes take place in the body as a result of repeated use of it. The UN World Health Organisation’s International Classification of Diseases 10 (ICD-10) describes  “dependence” in full. See this here. The ICD-10 doesn’t use “addiction” but it does “dependence” which is a broader term. On that link you will see the five criteria, of which three must be apparent for at least one month before “dependence” can be diagnosed. This covers the physical need, habituation, a psychological dependence, persistent use despite clear harmful effects, and progressive neglect of other pleasures.

Within this concept one cannot be “addicted” to cannabis but you can be “dependent”. To be addicted you must have a physiological need for a substance. To be “dependent” you can be covered by the strokes of a broader brush. Cannabis can cause dependence – fact. The Lancet’s position in 1998 suggested “About one in ten of those who ever use cannabis become dependent on it at some time during their 4 or 5 years of heaviest use.” This compares with alcohol (15%) but not with nicotine (32%) or opioids (25%).

Beyond mental illness there are other issues such as psychomotor impairment. Police are running out a new roadside test for drug use. Though not as bad as drink driving, you really shouldn’t smoke pot and drive. The Lancet piece leavens this somewhat by suggesting “studies of the effects of cannabis on driving under more realistic conditions on roads have shown much more modest impairments [than alcohol], probably because cannabis users are more aware of their impairment and less inclined to take risks than alcohol users.”

My own view is that cannabis isn’t the riskiest drug on the market. Every year that passes, so the understanding of the long term side effects of my antipsychotics are known. Cannabis doesn’t cause liver damage or diabetes, but the pills the doc gives me every night do. Cannabis doesn’t cause Sudden Death Syndrome – mine do. I’ve been taking this drug for 13 of the 18 years it has been licensed in the UK – studies on cannabis have been running since the 1960’s when they were giving people like me lobotomies through the eye sockets

However, medical science is taking great interest in cannabis for its medicinal properties. It is a relatively safe drug with high potential in medicine. I for one would love to try a 0% THC, high CBD strain to see if I could come off my antipsychotics one day. We never know, but maybe the stigma may fall enough that it is treated as the wonder drug it really should be!


Richard Shrubb

Richard Shrubb is a freelance journalist with a specific interest in medical science and sailing, for more info about Richard, see his web site www.richardshrubb.co.uk and you can follow Richard on Twitter #Shrubberz




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  1. That new zealand study does not agree with previous studies – Particularly Jamaican and Costa Rican studies that show no negative effects. So what were they smoking in NZ? Gritweed? pesticides? strains with unatural balance of thc/cbd? or was the study flawed in other ways – did it account for other factors, what about control group?
    And who funded it?
    Big pharma are known to lie about data and companies that rely on work from big pharma are unlikely to come up with the “wrong” results.

  2. So “What are the real risks of taking cannabis?”

    Reads to me that the risk is dependent on the user – for the very vast majority of users of pure cannabis, there is little or no risk of harm – but quite probably benefits. For a tiny number there may well be a greater risk for those predisposed to health problems.

    On the other hand “What are the real risks of taking cannabis bought on the illicit market?
    Risk from contamination, bad hygiene, adulteration.
    Risk of being offered other drugs.
    Risk of exposure to crime.
    Risk of arrest.
    Risk of criminal record.
    Risk of loss of job, career, income and home.
    Risk of restrictions from certain careers, travel to certain countries, insurance.

    Knock all them on the head by allowing people to cultivate cannabis in their own homes for their own use, and introduce licensed cultivation for retail to adults through commercial outlets where consumer protection and quality control is enabled, credible active available and taxation on profits.

    The you could write with confidence “The risk from cannabis is minimal”

  3. Cannabis effects and potency are much more complicated than the levels of two compounds (THC and CBD). There are many compounds that regulate it’s effects in combination.

    That said UK cannabis use is usually not just about cannabis use. It is most often tobacco mixed with cannabis – which takes a non-addictive, relatively harmless substance (cannabis) and makes it addictive and carcinogenic. The addictiveness of the UK ‘spliff’ culture leads to day long use (because of the tobacco addiction element) which in turn leads to social withdrawal and over use with the concomitant psychological effects. Especially for vulnerable people such as those predisposed to mental health problems or with unfulfilled and unproductive lives.

    Smoking cannabis is not the best method of ingestion but we need to educate people that if they choose this then not to mix it with tobacco. A vaporiser is better since the cannabis material is not burned. There is not reason, especially under a legalised system, that users could not move to a tablet form of cannabis, a drink or a food product – this method of ingestion causes very little harm at all.

    Illegally produced cannabis also contains many contaminants from poor production and storage methods that are dangerous to health. So in short inhaling tobacco, smoke, mould, chemical pesticides, fertiliser residue, bulking agents and cannabis is bad for you (what a surprise). Properly controlled and produced cannabis and cannabis extract products are relatively harmless – as is the experience with the US medical dispensaries – just ask our cousins in NORML USA.

    Hope this puts an end to the “is cannabis harmful ?” debate and it is all the more reason why we need to legalise, regulate and educate about cannabis.

  4. There are CBD extracts now, works for epilepsy maybe it could work for schizophrenia. But those are two total different things.

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