Regular cannabis users shaved 7000 years of healthy life off their cumulative lifespan in 2010. This may sound like a lot but it's just a drop in the ocean compared with the 9.2 million years opioid users lost, given that – at 16 million – 10 times fewer people use opioids than cannabis worldwide.
This is just one finding from the biggest epidemiological study of mental and substance-use disorders ever conducted, updating and significantly extending the first survey 20 years ago. The study, published in The Lancet, found that the burden caused by both mental and substance abuse disorders has increased significantly since 1990 but in the case of mental disorders, this was mainly the result of a growing population rather than any epidemic of poor mental health.
The results of the study should provide policy makers around the world with solid data on which to base health systems, says Louisa Degenhardt at the University of New South Wales in Australia, who led the part of the report looking at drug use.
Illicit drug use
Overall, the burden – defined as the number of healthy years of life lost because of illness, disability or early death – caused by illicit drug use increased by 52 per cent since the data was last collected. It jumped from 9.7 million years in 1990 to 17.2 million years in 2010. Worringly, about half of that increase was down to greater drug use, with population growth and an increase in the number of young people in developing countries accounting for the rest.
Cannabis is by far the most commonly used illicit drug in the world but accounts for an "absolutely tiny" health impact, says Degenhardt.
Even the modest disability caused by cannabis could be an exaggeration. The study assumed cannabis caused two disabling effects, both related to schizophrenia: causing it to start earlier and for its worst symptoms to last longer. But in an accompanying editorial, Michael Lynskey and John Strang from King's College London said that even these attributions might be regarded as controversial.
Opioids are the biggest cause of death and disability, accounting for half the illicit-drug burden, but it's also the drug class with the most effective measures to reduce its harm. Needle exchange programmes, opioid replacement therapy and HIV antiretroviral therapy could avert much of the damage, but sometimes communities are reluctant to embrace these, says Degenhardt.
A harder problem to deal with is cocaine and amphetamine use, for which proven treatments are more difficult to come by, the study authors note.
To some drug experts, the results show that current drug policies are failing. "This paper shows the cost of the dogged retention of the failed policy of drug prohibition," says Alex Wodak, a drug and alcohol researcher from St Vincent's Hospital in Sydney, Australia. "Why has the global implementation of needle syringe programmes and opioid substitution treatment been so unimpressive? Because they have been vehemently resisted by the supporters of global drug prohibition."
Mental health
The study also looked at the burden from mental disorders, which took into account those induced by substance use. It found that mental disorders are, as they were in 1990, the leading cause of non-fatal illness in the world. Back then, depression was the leading single cause of disability – now it is lower back pain.
Overall, the burden they cause is 37 per cent higher than it was in 1990, but most of that is down to a growing and greying population than a higher prevalence of mental illness per se. Harvey Whiteford from the University of Queensland, who led this part of the study, says that even if one perceives that life has become more stressful in the last 20 years, "there's no evidence that this is translating to a true increase in mental disorders".
Generally, rich countries had higher burdens than the global average because of their older populations. Countries embroiled in conflict also experienced higher than average burdens, with Afghanistan faring the worst of all. "Massive civil conflict like in Afghanistan and some African countries acts like an infectious disease – driving up prevalence," says Whiteford.
Only China, North Korea, Japan and Nigeria had burdens that were statistically lower than the global average. Whiteford suspects this might be a result of cultural differences in the way mental illness is expressed. "We are concerned that we have underestimated it for those countries because the Western instruments translated into those cultures fail to detect anxiety and depression," he says.
More resources will be needed to address mental disorders as life expectancy around the world rises, the authors conclude, since more people will be living for longer with such conditions. This will especially be the case in developing countries as the lifespans of their citizens increase. Some currently spend less than 2 per cent of their health budgets on mental health, compared with the 11 per cent spent in the UK or the 8 per cent in Australia.
But a big difference could be made at little cost. In sub-Saharan Africa, for example, the authors estimate the burden of depression could be reduced by between 10 per cent and 30 per cent for about $3 per head per year. "Primary care in developing countries is not expensive," says Whiteford. "Off-patent antidepressants are very cheap."
Journal reference: The Lancet, DOI: 10.1016/S0140-6736(13)61530-5; 10.1016/S0140-6736(13)61611-6
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, for example, at a party, but exactly how it does so is still up for debate.
