2026 ECNP Congress

PS04-4010

Quantifying the extent to which different levels of cannabis use can discriminate clinical thresholds of paranoia

Hannah Degen — R. Lees Thorne, E. Spinazzola, M. Di Forti, T. Freeman · University of Bath, Department of Psychology, Bath, United Kingdom

2026 ECNP Congress

Cannabis is one of the most widely used psychoactive substances globally [1], and its primary psychoactive compound, Δ9-tetrahydrocannabinol (THC) can produce psychotic-like experiences (PLEs) in otherwise healthy individuals [2]. Epidemiological evidence indicates a dose-response relationship between cannabis use and PLEs, with higher risk among early initiators [3]. A key limitation in this literature is reliance on crude exposure measures (e.g., lifetime use). Frequency of use captures patterns of consumptions, while other studies consider variation in cannabis potency (percentage of THC) and dose. The standard THC unit (5 mg THC) integrates frequency, potency and dose into a single standardised metric [4].

This study aimed to quantify the extent to which different levels of cannabis use can discriminate clinical thresholds of paranoia, a PLE characterised by persecutory ideation, using use frequency and standard THC units. Data were drawn from the Cannabis&Me general population sample in Greater London. Cannabis exposure was measured using self-reported use frequency and weekly THC units derived from reported quantity and potency. Potency estimates were based on Potter et al. [5], currently the best available UK estimates. Paranoia was assessed using Part B of the Green Paranoid Thoughts Scale (GPTS-B).

Associations between standard THC units and use frequency with paranoia were examined using multiple logistic regression adjusted for age, sex, ethnicity, education, and age at first cannabis use. Receiver operating characteristic (ROC) curve analyses assessed discrimination between higher and lower paranoia levels. Optimal thresholds were determined using Youden’s Index (maximum sensitivity + specificity), and AUC, sensitivity, and specificity were calculated at this point. Missing data (~10%) were handled using multiple imputation, and outliers were winsorised at the 95th percentile.

The final sample included 2,564 participants (66.5% male, mean age = 29.73 years). Mean GPTS score was 23.57, with n = 211 (8.23%) classified as higher paranoia. Mean weekly THC exposure was 203.46 units, and most participants reported daily use (1,684, 65,4%). Logistic regression showed that higher THC unit consumption was associated with increased odds of higher paranoia (p < .001), whereas frequency of use was not significantly associated with paranoia (all p > .06).

ROC analyses indicated modest discrimination for both the THC unit model (AUC = 0.65) and the frequency model (AUC = 0.64). At the optimal threshold, sensitivity and specificity were 72% and 45% for THC units (111.05), and 18% and 78% for frequency of use (4.5). For frequency, this threshold reflects a split between higher versus lower use categories rather than a continuous dose. In people using cannabis daily, THC units showed modest discrimination (AUC = 0.63) with sensitivity of 70% and specificity of 56% at an optimal threshold of 241.39.

Overall, THC exposure showed a consistent association with paranoia, whereas frequency did not. ROC analyses indicated modest discrimination for both measures, suggesting limited classification accuracy. These findings suggest that incorporating THC potency and quantity may improve understanding of paranoia risk at the group level, but overall association remains modest, and the ability to classify individuals at higher-risk is limited.

References

  1. United Nations Office on Drugs and Crime. (2024). World drug report 2024: Harms of world drug problem continue to mount amid expansions in drug use and markets. https://www.unodc.org/unodc/en/data-and-analysis/world-drug-report-2024.html
  2. Morgan, C. J. A., & Curran, H. V. (2008). Effects of cannabidiol on schizophrenia-like symptoms in people who use cannabis. British Journal of Psychiatry, 192(4), 306–307. https://doi.org/10.1192/bjp.bp.107.046649
  3. Belvederi Murri, M., Catania, S., Centra, S., Folesani, F., Muscettola, A., Zerbinati, L., Toffanin, T., Ferrara, M., Ossola, P., Rossi, R., Jannini, T., Caruso, R., Nanni, M. G., & Grassi, L. (2025). The association between cannabis use and paranoia: Meta-analysis of experimental and observational studies. Neuroscience & Biobehavioral Reviews, 176, 106269. https://doi.org/10.1016/j.neubiorev.2025.106269
  4. Freeman, T. P., & Lorenzetti, V. (2020). ‘Standard THC units’: A proposal to standardize dose across all cannabis products and methods of administration. Addiction, 115(7), 1207–1216. https://doi.org/10.1111/add.14842
  5. Potter, D. J., Hammond, K., Tuffnell, S., Walker, C., & Di Forti, M. (2018). Potency of Δ9–tetrahydrocannabinol and other cannabinoids in cannabis in England in 2016: Implications for public health and pharmacology. Drug Testing and Analysis, 10(4), 628–635. https://doi.org/10.1002/dta.2368