One in Five Research Participants Underreported Drug Use When Checked Against Hair Tests
About 21% of participants denied using a substance that their hair test detected, highlighting the limits of relying on self-report alone in research.
Quick Facts
What This Study Found
21.3% of 75 participants underreported use of at least one substance (negative self-report but positive hair test). For cannabis specifically, self-reported frequency and quantity predicted THC detection in hair, but years of use and time since last use did not.
Key Numbers
21.3% underreported at least one substance; moderate-to-large effect sizes observed for MDMA and cocaine discordance; cannabis use frequency and quantity predicted THC hair detection; years of use and time since last use did not predict detection
How They Did This
75 adults completed substance use questionnaires and provided hair samples analyzed by liquid chromatography-mass spectrometry for drug detection over the prior 3 months. Underreporting was defined as denying use while testing positive.
Why This Research Matters
Cannabis research depends heavily on self-reported use, but this study shows that more than one in five people may deny use that biological testing confirms. This has direct implications for how we interpret survey-based cannabis research.
The Bigger Picture
If roughly one-fifth of research participants underreport substance use, studies relying solely on self-report may systematically underestimate cannabis use prevalence and misclassify participants, potentially skewing findings across the field.
What This Study Doesn't Tell Us
Small sample (75 participants), hair testing has its own limitations (can miss very light use, affected by hair treatments), no data on why participants underreported, single timepoint
Questions This Raises
- ?Would underreporting rates differ in clinical vs. research settings?
- ?Do legal status and social stigma affect underreporting rates for cannabis specifically?
- ?Could combined self-report and biological measures become standard in cannabis research?
Trust & Context
- Key Stat:
- 21.3% of participants denied using a substance that their hair test detected
- Evidence Grade:
- Small cross-sectional study comparing two measurement methods; provides useful methodological insights but limited sample size
- Study Age:
- Published 2025
- Original Title:
- Substance use assessment: comparing self-reports with objective data in a research setting.
- Published In:
- Frontiers in public health, 13, 1628519 (2025)
- Authors:
- Binkowska, Alicja Anna, Pałczyński, Piotr, Jakubowska, Natalia, Czarny, Jakub, Raczkowski, Michał, Brzezicka, Aneta
- Database ID:
- RTHC-06068
Evidence Hierarchy
A snapshot of a population at one point in time.
What do these levels mean? →Frequently Asked Questions
How accurate are self-reports of cannabis use in research?
In this study, about 1 in 5 participants denied using a substance that their hair test detected, suggesting self-reports alone may underestimate actual use.
Does how often someone uses cannabis predict whether a hair test will find THC?
Yes. Self-reported frequency and quantity of cannabis use predicted THC detection in hair, but total years of use and time since last use did not.
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Cite This Study
https://rethinkthc.com/research/RTHC-06068APA
Binkowska, Alicja Anna; Pałczyński, Piotr; Jakubowska, Natalia; Czarny, Jakub; Raczkowski, Michał; Brzezicka, Aneta. (2025). Substance use assessment: comparing self-reports with objective data in a research setting.. Frontiers in public health, 13, 1628519. https://doi.org/10.3389/fpubh.2025.1628519
MLA
Binkowska, Alicja Anna, et al. "Substance use assessment: comparing self-reports with objective data in a research setting.." Frontiers in public health, 2025. https://doi.org/10.3389/fpubh.2025.1628519
RethinkTHC
RethinkTHC Research Database. "Substance use assessment: comparing self-reports with object..." RTHC-06068. Retrieved from https://rethinkthc.com/research/binkowska-2025-substance-use-assessment-comparing
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.