The first ever analysis of the global and regional prevalence of dependence upon the four major categories of illicit drugs - amphetamine, cannabis, cocaine, and opioids (such as heroin) - has revealed that opioid dependence causes the greatest health burden (overall death and illness) of all the illicit drugs. The results come from new analysis of the Global Burden of Disease Study 2010, and are published in The Lancet.
For all of the drugs studied, over two thirds of dependent individuals were male (64% each for cannabis and amphetamines, and 70% each for opioids and cocaine). All forms of drug dependence and disease burden were highest in men aged 20 - 29 years.
Led by Professor Louisa Degenhardt, a team of researchers in Australia and the US performed a comprehensive search of available data on the prevalence and effects of amphetamines, cannabis, cocaine, and opioids. Other drugs, including MDMA (ecstasy) and hallucinogens such as LSD, were not included separately in the analysis due to a lack of high quality data on their prevalence and health effects.
The results show that the burden in the worst affected countries (largely high-income nations such as USA, UK, and Australia) was 20 times greater than in the least affected countries. Regional breakdown of the results shows that the highest prevalence of cocaine dependence was in North America and Latin America, and among the highest levels of opioid dependence were in Australasia and Western Europe. The UK, USA, South Africa, and Australia all had notably high overall burdens of death and illness due to illicit drugs.
Although the results show that cannabis is by far the most commonly used illicit drug worldwide, the prevalence of cannabis dependence (13.0 million people worldwide) was somewhat lower than for amphetamines (17.2 million) and opioids (15.5 million), the two most common forms of illicit drug dependence.
The biggest source of burden of disease was opioid dependence, followed by amphetamine dependence, and injecting drug use as a risk factor for blood-borne viruses (hepatitis B, C, and HIV). Cannabis and cocaine dependence were more modest sources of disease burden, due to the smaller size of these populations and the lower levels of disability associated with these drugs.
By using the same methods to estimate burden in 1990 in this study, the researchers were also able to examine trends over time. They found that disability and illness caused by the four drugs studied has increased by over 50% between 1990 and 2010. Although some of this increase is due to increasing population size, over a fifth (22%) of the increase is thought to be due to increasing prevalence of drug use disorders, particularly for opioid dependence. Of around 78000 deaths in 2010 attributed to drug disorders, more than half (55%) were thought to be due to opioid dependence.
Despite the substantial preventable disease burden found to be attributable to the four drugs studied, their overall burden is still less than that of smoking and alcohol, which are together responsible for around 10% of the total death and illness burden worldwide. The new study estimates that illicit drug dependence contributes to just under 1% of the total global burden of death and illness. However, given the large differences in the prevalence of illicit drug dependence compared to alcohol dependence and tobacco use, it is clear that illicit drug use causes comparatively more burden per person.
According to Professor Degenhardt, "Although this study made use of advanced modelling to impute results when data were not available, a substantial amount of research is needed to document even the most basic epidemiological parameters for drug dependence in most countries. Until such work is done, much uncertainty will remain around the exact size of global disease burden attributable to illicit drug use."*
"However, our results clearly show that illicit drug use is an important contributor to the global disease burden, and we now have the first global picture of this cause of health loss. Moreover, much can be done to reduce this burden. Although we have fewer means of responding to some causes of burden, such as cocaine and amphetamine dependence, well-evaluated and effective interventions can substantially reduce two major causes of burden - opioid dependence and injecting drug use. The challenge will be to deliver these efficiently and on a scale needed to have an effect on a population level."*