Beyond a spec: assessing heterogeneity in the unregulated opioid supply.

BACKGROUND: Drug checking services aim to provide compositional information for the illicit drug supply and are being employed in public health responses to extreme rates of overdose associated with fentanyl within street opioids. The technologies used within these services range from basic qualitative tests, such as immunoassay test strips, to comprehensive quantitative analyses, such as mass spectrometry. In general, there is concern that heterogeneity of a drug mixture adds significant uncertainty when using drug checking results based on a small subsamples. The presence of hot spots of active drug components in this context is often termed the 'chocolate chip cookie effect'. Establishing the limitations of the service are essential for interpretation of the results. METHODS: This study assesses the consequence of drug heterogeneity and sampling of consumer level opioid purchased in Victoria, British Columbia ( n = 21 , 50-100 mg each) on quantitative fentanyl results determined from testing with paper spray mass spectrometry. RESULTS: Using descriptive statistics, such as relative standard deviation and interquartile range, the results demonstrate varied distributions of fentanyl concentrations within a single drug batch. However, the presence of hot spots, defined as outliers, were relatively rare. CONCLUSIONS: This study found that the variability in fentanyl concentration from drug heterogeneity and sampling is greater than that attributed to the analytical technique. On a practical level, this provides data to help guide communication of limitations of drug checking services, supporting the aim of trust and transparency between services and people who use drugs. However, if drug checking services continue to be restricted from fully engaging with the reality of manufacturing, buying, selling, mixing and dosing practices, the accuracy, usefulness, and impact will always be limited.

Identity-specific neural responses to three categories of face familiarity (own, friend, stranger) using fast periodic visual stimulation.

Previous studies have focused on the modulatory effects of face familiarity on different components of an event-related potential (ERP), but there is controversy in the literature regarding the precise component that reflects the process of identity recognition. This may be partly explained by limits to this waveform analysis approach, as waveforms elicited by the presentation of a face are likely to reflect a variety of different cognitive processes that overlap in time. Using fast periodic visual stimulation and EEG (FPVS-EEG), we directly measured the electrophysiological response reflecting identity-specific recognition after isolating it from responses attributable to low-level visual processing and face-selective processes that are not identity-specific. The observed response therefore provides a robust and objective measure of the recognition of a personally familiar face generated bilaterally in the occipito-temporal region. We tested the magnitude of this identity-specific response to three categories of familiarity: the own-face (high familiarity), a friend's face (moderate familiarity), and a stranger's face (no familiarity). We found the largest response to the participant's own-face, followed by an intermediate response to a highly personally familiar face, and the smallest response to an unfamiliar face. An additional response was observed over the posterior cortical midline for familiar faces only, consistent with theories that familiar identity recognition also triggers post-perceptual semantic processing.