In a clinical trial of 1,285 emergency department drug users, hair analysis and self-reported drug use showed high agreement for cannabis and street opioids, but poor agreement for cocaine and prescribed opioids.
Read this if you work in addiction research or clinical trials and want to know how reliable self-reported cannabis use is.
High concordance between hair analysis and self-report for cannabis across 3, 6, and 12 month assessments.
What the researchers found
Researchers compared hair analysis results with self-reported drug use (Timeline Follow Back) for four drug classes across 1,285 adult emergency department patients with moderate to severe drug problems.
Hair analysis and self-report showed high concordance for cannabis and street opioids but low to moderate concordance for cocaine and prescribed opioids. An important pattern emerged: people were significantly more accurate in reporting their primary drug of choice. Under-reporting of use given a positive hair test was always lower for the person's primary drug compared to secondary drugs.
Conversely, over-reporting of use given a negative hair test was higher for the drug of choice, suggesting some people reported using their preferred drug more than they actually did, or that hair analysis may not capture all patterns of use.
Why it matters
Clinical trials of addiction treatments rely on self-reported drug use, and there are longstanding concerns about accuracy. This study demonstrates that for cannabis specifically, self-report is quite reliable when compared to biological verification via hair analysis. This validates cannabis use data from clinical trials that relied on self-report.
The numbers in context
1,285 participants from 6 US academic hospitals. High concordance for cannabis and street opioids. Low to moderate concordance for cocaine and prescribed opioids. Under-reporting was always lower for the participant's primary drug of choice.
How the study worked
Secondary analysis of a National Drug Abuse Treatment Clinical Trials Network randomized trial (NCT01207791). 1,285 adult ED patients with moderate to severe drug problems were assessed at 3, 6, and 12 months. Both hair analysis and Timeline Follow Back self-reports covered the same 90-day periods.
What this study cannot tell us
The sample consisted of people with moderate to severe drug problems presenting to emergency departments, which may not represent all drug users. Hair analysis itself has limitations: it may not detect very light use, results can be affected by hair treatments, and some populations may decline to provide hair samples. The 90-day recall window is long for self-report accuracy.
How to read the evidence
Moderate evidence from a large multi-center clinical trial with both biological and self-report measures collected at multiple time points.
When this study was published
Published in 2016. Hair analysis methodology and self-report instruments continue to be refined.
The bigger picture
The reliability of self-reported drug use is a fundamental question in addiction research. This study provides reassurance that cannabis self-reports are generally trustworthy, while highlighting that cocaine and prescribed opioid self-reports should be verified with biological measures when accuracy is critical.
Questions still open
- Why is concordance higher for cannabis than cocaine? Is it because cannabis stays in hair longer, because cannabis use is more routine and therefore easier to recall, or because cocaine use is more stigmatized? Would newer drug testing methods (oral fluid, sweat patches) show different concordance patterns?
Common questions
Do people accurately report their cannabis use?
Can hair tests detect cannabis use?
Read the original research
Hair analysis and its concordance with self-report for drug users presenting in emergency department.
Drug and alcohol dependence, 167, 149-55
Citation
Sharma, Gaurav; Oden, Neal; VanVeldhuisen, Paul C; Bogenschutz, Michael P. (2016). Hair analysis and its concordance with self-report for drug users presenting in emergency department.. Drug and alcohol dependence, 167, 149-55. https://doi.org/10.1016/j.drugalcdep.2016.08.007
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