BBC Future

The Real Risk

Highs and lows of illegal drugs

About the author

David Spiegelhalter is Winton Professor of the Public Understanding of Risk at the University of Cambridge, UK. His professional background is in medical statistics. He is a frequent contributor to the media, and has been an advisor on risk issues as diverse as breast implants, volcanic ash, clinical trials, surgical mortality, and the inquiry into mass murderer Harold Shipman. He is a Fellow of the Royal Society and was awarded an OBE in 2006. You can see more of David’s explorations of risk at the Understanding Uncertainty website, or follow him on Twitter at @undunc

Risks of illegal drug use

(Copyright: Science Photo Library)

Our resident statistician David Spiegelhalter sifts through the data to discover how much is being swallowed, smoked, snorted or injected.

People have taken mood-altering substances in various forms since time began. Remains of opium poppy husks have been found in Neolithic settlements in Europe; natives of South America have long chewed coca leaves as a mild stimulant or to suppress pain; almost everything faintly edible has been fermented to make alcohol.

Drug production went from cottage to factory industry from the late 1820s onwards, with Heinrich Merck’s commercialization of morphine, an extract from opium. This laid the foundation for the pharmaceutical company that still bears his name, Merck. Heroin, also known as diamorphine, was first derived from morphine in St Mary’s Medical School in London in 1874, but rediscovered by the Bayer pharmaceutical company in 1897, and marketed as a non-additive painkiller and cough medicine.   

Meanwhile, cocaine was extracted from coca leaves and found widespread usage: one product available for children in the late 1800s claimed Cocaine toothache drops. Instantaneous cure!  Sigmund Freud was one of many cocaine enthusiasts, as was Sherlock Holmes, much to Dr Watson’s frequent disgust.

User behaviour

From the early 20th century onwards, increasing pressure based on addictive properties of opiates and cocaine saw criminalisation for misuse. Among the many implications and consequences of such measures, it makes it tricky for us statisticians nowadays to find out how much is being swallowed, smoked, snorted or injected.

The 2011 world drug report by the UN Office on Drugs and Crime (UNODC) illustrates this difficulty; the report estimates that between 149 million and 271 million people aged 15-64 years had used an illicit drug at least once in 2009. That’s between 3.3 and 6.1% of the global population. Around 125-203 million were cannabis users (2.8-4.5% of the global population), between 14 and 56 million people (0.3-1.3%) used an amphetamine-style stimulant, 14-21 million (0.3-0.5%) used cocaine, and 12-21 million were opioid users.

The best data on drug use come from developed countries in Europe, North America and Australasia. For instance, the British Crime Survey (BCS) guarantees anonymity when it asks about use of illegal drugs. Responses scaled up to the adult (16 to 59) population of England and Wales show around one in three are estimated to have used illegal drugs in their lifetime, with around 9% using them in the past year. Men are about twice as likely to be users than women, and an unsurprising relationship found between nightclub and pub visits and illicit drug use. I could have told them that for free.

I could also tell them for free that these drugs can certainly be dangerous in the wrong hands: Manchester general practitioner Harold Shipman injected over 200 of his patients with lethal doses of diamorphine (heroin) in his murderous career, before he was finally caught in 1998 due to a clumsy forgery of a will.  And there are numerous famous deaths due to drug overdoses, whether deliberate or not, from Janis Joplin to the Singing Nun.

Death threat

But working out exactly how many people die due to misuse of illegal drugs is difficult: generally a mention on the death certificate means the death is considered as drug-related, even if not solely due to the drug.

Taking the England and Wales figures as an example, there were 1,784 deaths in 2010 from misuse of illegal drugs, without alcohol specifically mentioned, down a bit from preceding years, but double that in 1993. The peak decade is for men in their 30s with 544 deaths in a year, that’s about one for every 680 men in this age band.   Almost exactly half the total deaths (791) were due to heroin or morphine.  Cocaine was associated with 144 deaths, amphetamine 56, while those involving ecstasy (MDMA) fell to only eight after averaging around 50 a year from 2001 to 2008.

If we use the British Crime Survey estimates of the number of users, we can get a rough idea of the annual risk of using different drugs in micromorts (that is, the chance in a million of dying).

Averaging over the period between 2003 and 2007, cocaine and crack cocaine were involved in 169 deaths per year, and so an estimated 793,000 users were each exposed to an average of 213 micromorts a year, or around four a week. Ecstasy’s 541,000 users experienced around 91 micromorts a year each: the 2003 market for Ecstasy has been estimated as 4.6 tonnes, corresponding to around 14,000,000 tablets, or an average of around 26 per user. This translates to around 3.5 micromorts per tablet.

Cannabis rarely directly leads to death, but its estimated 2,800,000 users suffered an average of 16 associated deaths per year, which is 6 micromorts a year. The average of 766 heroin-related deaths a year comes out as 19,700 micromorts per year – 54 a day – but this will be an underestimate. 

But there are many other harmful effects apart from death: for example, it’s been estimated that smokers of cannabis are about 2.6 times more likely to have a psychotic-like experience than non-smokers. Apart from the risks of dependence and withdrawal, heroin users may get HIV or hepatitis from non-sterile needles, or abscesses and poisoning with contaminants. Not forgetting the standard effect of opiates on chronic constipation.

Risk status

So how can we compare the harms of different drugs, including legal ones such as alcohol and tobacco? A study published in 2010 looked at harms to users, such as mortality, damage to physical and mental health, dependence, and loss of resources and relationships, as well as harms to society, such as injury of others, crime, environmental damage, family adversities, international damage, economic cost and effects on the community. Each drug was scored on each dimension, the different harms weighted according to their judged importance and a total harm score calculated. 

The resulting ranking put alcohol at the top with 72, then heroin and crack cocaine at 55 and 54, tobacco was 6th at 26, and ecstasy almost at the bottom of the list with nine, in spite of it being a Class A drug in the UK. This was controversial, with one national UK tabloid newspaper proclaiming that the main author, Professor David Nutt, was a ‘dangerous man’.

Even more controversial than comparing illegal and legal drugs, is to compare illegal drugs with ‘wholesome’ activities.  Again it was Nutt, then head of the Advisory Council for the Misuse of Drugs (ACMD), who wrote a paper comparing ecstasy with ‘equasy’, the addiction to horse-riding, claiming that these were both voluntary leisure activities of young people, and of comparable dangers.  He did not stay as head of the ACMD for much longer.

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