Comparative risk assessment for illicit drug use
Risk factor definition in the GBD
For the Global Burden of Disease (GBD) study, there is investigation of illicit drug use as a risk factor for disease and injury. The GBD defines risks according to the following considerations:
- Risk factors should be potentially modifiable;
- Risks should be assessed irrespective of place in a causal chain or scientific discipline that has traditionally analysed the risk factor, as long as evidence of causal effect can be established;
- Risks are defined to be not too broad (e.g. diet or environment as a whole) or too narrow (e.g. every single fruit and vegetable or every toxicant in tobacco smoke) with a relatively specific definition of risk factor exposure;
- Protective as well as hazardous factors are considered. However, the absence of a specific intervention should not be assessed as a risk factor, but rather in measurement of intervention coverage and effectiveness; and
- There exists sufficient data on risk factor exposure and risk-factor disease relationships.
Exposure variable for illicit drug use in the GBD
The risk of premature mortality and morbidity from illicit drug use is dependent on dose, frequency and route of administration. Consequently, it is necessary to define what is meant by “use” when defining the exposure variable “illicit drug use”. The mortality risks of illicit drug consumption increase with increasing frequency and quantity of consumption
1. Simple prevalence estimates of the proportion of the population that have
ever used an illicit drug are likely to be associated with a low average risk since a single occasion of use and infrequent use, the most common patterns of use reported in population surveys, are associated with a small increase in mortality. More accurate estimates of the burden of disease attributable to illicit drugs require estimates of the prevalence of the most hazardous patterns of illicit drug use. These are found in highest prevalence among dependent drug users who typically inject drugs daily or near daily over periods of years. This pattern of use exposes users to the highest chance of fatal overdose
2 and of contracting blood borne viral diseases
3.
The World Health Organization (WHO), following the International Classification of Disease, defines problem drug use as “harmful drug use” and “drug dependence”. Harmful drug use is defined by clear evidence that the substance use is responsible for physical (e.g. organ damage) and psychological harm (e.g. drug-induced psychosis). Drug dependence, as defined in ICD-10, requires the presence of three or more indicators of drug dependence
4. These include: a strong desire to take the substance; impaired control over the use; a withdrawal syndrome on ceasing or reducing use; tolerance to the effects of the drug; requiring larger doses to achieve the desired psychological effect; a disproportionate amount of the user’s time is spent obtaining, using and recovering from drug use; and the user continuing to take other drugs despite associated problems. The problems should have been experienced at some time during the previous year for at least one month.
The United Nations Office on Drugs and Crime (UNODC) identifies “problem drugs” based on “the extent to which use of a certain drug leads to treatment demand, emergency room visits (often due to overdose), drug-related morbidity (including HIV/AIDS, hepatitis etc.), mortality and other drug-related social ills”
5.
Most prevalence estimates vary with the assumptions made and the methodology employed. Data provided by the UNODC
6 do not have the same reliability as large-scale household surveys of the type generally conducted in developed countries. Unfortunately the expense of conducting such surveys makes their use in developing countries unfeasible. Even if such surveys were feasible in all countries, it is generally accepted that surveys underestimate harmful illicit drug use
7.
The European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) has invested considerable resources in developing methods for the collection of data on the prevalence of harmful illicit drug use that are both valid and comparable
8. Although these standards have been developed for use within the European Union, the global adoption of such standards may greatly improve estimates of drug-related harm. The EMCDDA defines “problem drug use” as
injecting drug use (IDU) or long duration or regular use of opioids, cocaine or amphetamines9.
This is the term that will be used for estimation of risk for: HIV, hepatitis C, suicide, and trauma. In the previous comparative risk assessment exercise, there was no estimation of cannabis use as a risk factor for disease burden
10.
Regular or dependent cannabis use will be considered in the estimates made for the CRA exercise for cannabis.
Counterfactual exposure distribution
The
theoretical minimum counterfactual exposure distribution is zero illicit drug use. There may be countries in the world that can truly claim to have zero illicit drug use but there must be few of these now. Even countries that have the policy aim of achieving a drug-free society, such as Sweden, do not have zero illicit drug use. Arguably, once illicit drug use and dependence have appeared in a society, it is unrealistic to expect to be able to return to a zero level of illicit drug use. It may be reasonable to aim to reduce the prevalence of some types of illicit drug use and to minimize the harm that it causes.
One approach to defining a
plausible counterfactual exposure would be to use developed countries with the lowest prevalence of illicit drug use as the basis for the estimate. Countries like Finland and Sweden may be suggested as examples. The weakness with this strategy is that illicit drug use trends are dynamic and countries that currently have low rates may show increases in rates of use (as has recently happened in Sweden) as availability of illicit drugs increases and more favourable social attitudes develop towards illicit drug use.
It is also not clear what are feasible minimum counterfactuals. It is not clear whether prevention programmes, such as school-based and other intervention programmes, can prevent problem drug use
11. These programmes have been most widely implemented and evaluated in the United States. After reviewing this evidence, the United States National Research Council recently concluded that the
“effectiveness of most of these approaches for reducing substance use is unknown…Some prevention approaches are effective at delaying the initiation or reducing the frequency of tobacco, alcohol and marijuana use [but]…the magnitude of these effects are generally small…[and it] is not clear that preventing or reducing the use of gateway substances translates into a reduced use of cocaine or other illegal drugs” (pp. 233–234).
These conclusions have been supported by a study of the likely impact of the most effective school-based preventive programmes, which concluded that they would have, at best, very modest effects in preventing cocaine use
12.
There is better evidence that some treatment programmes (e.g. opioid agonist maintenance treatment) can substantially reduce illicit opioid use and premature mortality from drug overdose among opioid-dependent persons
2. In the case of opioid-dependent persons, one could examine the effects that enrolling 10%, 20%, 30%, etc. of persons who were dependent on illicit opioids in opioid maintenance treatment would have on illicit opioid use, overdose deaths and disability produced by illicit opioid dependence. Similar estimates could be made of the expected reduction in HIV/AIDS among injecting drug users from the introduction of needle and syringe exchange and distribution programmes.
Discussion papers
A discussion paper on the injuries/diseases to be included in the comparative risk assessment for regular cannabis use is available. Click
here to access this paper.
A discussion paper on injecting and "problem" drug use as a risk factor will be available soon.
A discussion paper on illicit drugs as risk factors is available. Click
here to access this paper.
References
1. Fischer B, Kendall P, Rehm J, Room R. Charting WHO-goals for licit and illicit drugs for the year 2000: are we "on track"?
Public Health 1997;111:271-275.
2. Warner-Smith M, Darke S, Lynskey M, Hall W. Heroin overdose: causes and consequences.
Addiction 2001;96(8):1113-1125.
3. Ross M, Wodak A, Loxley W, Stowe A, Drury M. Staying negative. Summary of the results of the Australian National AIDS and Injecting Drug Use Study. Sydney: ANAIDUS, 1992.
4. World Health Organization.
The ICD-10 Classification of Mental and Behavioural Disorders - Diagnostic Criteria for Research. Geneva: World Health Organization, 1993.
5. UNDCP. Global Illicit Drug Trends 2000. Vienna: United Nations Drug Control Programme, 2000.
6. United Nations Office on Drugs and Crime. World Drug Report 2006. Vienna: United Nations, 2007.
7. Hall W, Ross J, Lynskey M, Law M, Degenhardt L. How many dependent heroin users are there in Australia? NDARC Monograph No. 44. Sydney: National Drug and Alcohol Research Centre, UNSW., 2000.
8. EMCDDA. Estimating the prevalence of problem drug use in Europe. Luxembourg: European Monitoring Centre for Drugs and Drug Addiction, 1997.
9. EMCDDA. Study to Obtain Comparable National Estimates of Problem Drug Use Prevalence for all EU Member States. Lisbon: European Monitoring Centre for Drugs and Drug Addiction, 1999.
10. Degenhardt L, Hall W, Lynskey M, Warner-Smith M. Chapter 13. Illicit drug use. In: Ezzati M, Lopez AD, Rodgers A, Murray R, editors.
Comparative Quantification of Health Risks: Global and Regional Burden of Disease Attributable to Selected Major Risk Factors. 2nd edition ed. Geneva: World Health Organization, 2004:1109-1176.
11. National Research Council. Informing America's Policy on Illegal Drugs: what we don't know keeps hurting us. Washington: National Academy Press, 2001.
12. Caulkins J, Rydell C, Everingham S.
An ounce of prevention, a pound of uncertainty. The cost effectiveness of school-based drug prevention programs. Santa Monica, CA: Drug Policy Research Center, 1999.