INTRODUCTION: Drug checking services (DCS) provide people with information about the contents of their drugs, reducing uncertainty about the composition of substances from unregulated markets. However, their impact on behaviour change has been sparsely evaluated. This study aimed to assess behaviour change following receipt of a drug checking result among users of French DCS.

METHODS: Data were drawn from ChecKnow, a French e-cohort of people who use drugs. Using cross-sectional, baseline survey data, we identified participants who accessed face-to-face DCS within the previous 6 months. Reported drug checking results were categorised as containing only the expected substance, a non-psychoactive diluent, a psychoactive adulterant, or an entirely different substance. We assessed whether discordance between participants' drug checking result and their expectation was associated with subsequent engagement in risk-reducing behaviour, using Poisson regression adjusted for relevant confounders.

RESULTS: A total of 1363 participants completed the survey and 480 (35.2%) reported ever using DCS. Compared to results containing only the expected substance, the prevalence of engaging in risk-reducing behaviour increased with each category: diluted (adjusted prevalence ratio [aPR] = 2.78; 95% confidence interval [CI] 0.84, 9.18), adulterated (aPR = 3.34; 95% CI 1.52, 7.34) and absent (aPR = 5.48; 95% CI 2.61, 11.50).

DISCUSSION AND CONCLUSIONS: Receipt of unexpected drug checking results was associated with a graded increase in the likelihood of engaging in risk reduction behaviours, with the strongest effects observed when the expected substance was entirely absent. These findings suggest that DCS may effectively promote behavioural adaptation in response to potential drug-related risks.