# Cannabis Use and Suicidal Behaviour in Young Adults Across Washington State and Victoria > **Author:** Benjamin Caplan, MD (ABFM Board Certified, MA Lic. #240562, NPI: 1962722637) > **Publisher:** CED Clinic (https://cedclinic.com) > **Canonical URL:** https://cedclinic.com/ced-cannabis-use-and-suicidal-behaviour-2026-09-25/ > **Published:** 2026-09-25T17:41:26-04:00 | **Last Modified / Clinically Audited:** 2026-10-01T12:33:06-04:00 > **Clinical Summary:** medical cannabis research: Physician review of Longitudinal Effects of Cannabis Use on Suicidal Behaviour in Early Adulthood in Washington State, United Stat... --- CED Clinical Relevance #88 Verified Clinical Evidence Primary literature analysis of Longitudinal Effects of Cannabis Use on Suicidal Behaviour in Early Adulthood in Washington State, United States and Victoria, Australia. Clinical Insight | CED Clinic This study is clinically important because it separates two questions that are often conflated: whether cannabis use is associated with suicidal behaviour, and whether legalization itself explains population-level suicidal behaviour. In 1,470 young adults followed from about age 25 to 29, cannabis use and increasing use were associated with later suicidal behaviour, even after multivariable and propensity approaches. Yet Washington State, where recreational cannabis was legal, had higher cannabis use but lower self-harm at age 29 than Victoria. Clinically, this supports careful screening for mood symptoms, self-harm history, substance co-use, and escalation of cannabis consumption, rather than simplistic conclusions about cannabis law alone. Clinical SciencePeer-ReviewedDosing ContextSafety SignalsPhysician Insight AudiencePatients, clinicians, healthcare providers, researchers, and policy analysts. Primary TopicClinical study review: Cannabis Use and Suicidal Behaviour in Young Adult. Source[Read the full source](https://pubmed.ncbi.nlm.nih.gov/42782471/) A longitudinal cohort study linked young adult cannabis use with later suicidal behaviour, while also showing that legalization context alone did not explain regional suicide risk patterns. What This Study Teaches Us In 1,470 International Youth Development Study participants, 726 from Victoria and 744 from Washington State, cannabis use at mean age 25 and increased use by mean age 29 predicted increased suicidal behaviour in multivariate negative binomial and propensity score analyses. Washington State participants reported higher past-year cannabis use at age 25 and increasing use through age 29, yet lower self-harm at age 29 than Victorian participants. Why This Matters For patient care, the signal is strongest around escalating use and prior suicidal behaviour, both of which should trigger more careful psychiatric screening and follow-up. For counseling, this study argues against both dismissal of risk and simplistic claims that legalization alone explains suicidal behaviour. Study SnapshotPost TypePhysician-Guided Clinical Science Deep DivePrimary SourcePrevention science: the official journal of the Society for Prevention ResearchPublication Date2026Sep24Evidence LevelJournal ArticleFocus AreaCannabis Use and Suicidal Behaviour in Young Adults Across WLead AuthorsAbbey J Fitzpatrick, Jessica A Heerde, Bosco Rowland, Ebru A Batmaz et al.DOI10.1007/s11121-026-01987-zPMIDPMID: 42782471 Clinical Bottom Line This study review translates complex data into practical clinical insights, maintaining realistic therapeutic expectations. Headline vs. Reality Truth Meter | Clinical Analysis **Mainstream Media Claim:** Legal cannabis causes suicidal behaviour in young adults. **Primary Journal Data:** The study found that cannabis use at age 25 and increased cannabis use by age 29 predicted higher suicidal behaviour in longitudinal models. However, Washington State had higher cannabis use and still showed lower self-harm at age 29 than Victoria, suggesting multiple regional, social, psychiatric, and policy determinants. **Dr. Caplan’s Clinical Verdict:** The evidence supports cannabis use as a clinically relevant risk marker for suicidal behaviour in early adulthood, especially when use increases. It does not prove that legalization alone causes suicidality, nor that all cannabis exposure carries the same risk. Primary Analysis | Longitudinal Effects of Cannabis Use on **Study Overview:** This study aimed to investigate the impact of cannabis use on young adult suicidal behaviour. Matched cohorts were compared across two regions: Washington State, USA (where recreational cannabis use was legalised in 2012) and Victoria, Australia (where recreational cannabis use remains illegal). The hypotheses were (1) cannabis use would be more prevalent in Washington State in association with legalisation and (2) cannabis use would predict suicidal behaviour similarly in both regions. Data were drawn from the International Youth Development Study (IYDS) involving 1,470 participants (55.4% female; 726 Victoria, 744 Washington State) surveyed at average ages 25 and 29 in 2014 and 2018, respectively. Participants completed self-report surveys assessing demographic data, cannabis use, other forms of substance use, proximity to cannabis sales outlets, and suicidal behaviour. Data were analysed using multivariate negative binomial regression to identify cannabis use predictors of incident suicidal behaviour and differences between the two regions. Washington State participants reported significantly higher past-year cannabis use compared to Victorian participants at age 25 (in 2014) and lower self-harm at age 29 (2018). Victorian participants reported a reduction in cannabis use from age 25 to 29, while increased use was reported by Washington State participants across the same period. Regression analysis showed higher rates of cannabis use at 25 years and increased cannabis consumption at 29 years predicted increased suicidal behaviour. Suicidal behaviour in 2014 predicted this behaviour in 2018, with higher predictive risk in Washington State. Propensity score analysis confirmed a significant effect of cannabis use on suicidal behaviour. The effect of legalisation indicators (Washington State location, proximity to cannabis stores) on cannabis use was also significant based on propensity analysis. Cannabis was more prevalent in Washington State through the late 20 s. Young adult cannabis use increased the likelihood of suicidal behaviours. Despite increased risk from cannabis use, Washington State maintained lower rates of suicidal behaviour compared to Victoria, emphasising the need to understand multiple determinants of state differences in suicidal behaviour. **Primary Source & Scope:** Published in *Prevention science: the official journal of the Society for Prevention Research* (2026Sep24) conducted by Abbey J Fitzpatrick, Jessica A Heerde, Bosco Rowland, Ebru A Batmaz et al. [Primary Source Link](https://pubmed.ncbi.nlm.nih.gov/42782471/) | **Primary Record:** DOI: 10.1007/s11121-026-01987-z | PMID: 42782471 How Strong Is This Evidence? This is a longitudinal matched cohort analysis using 1,470 participants from two regions, with repeated measures at approximately ages 25 and 29. The use of multivariate negative binomial regression and propensity score analysis strengthens causal inference compared with a simple cross-sectional survey, although it remains observational. The binational policy contrast adds practical relevance, but the abstract does not provide full effect sizes, confidence intervals, or model covariate performance. Where This Paper Deserves Skepticism Cannabis use, suicidal behaviour, and other substance use were self-reported, which may introduce recall bias, stigma-related underreporting, and regional differences in disclosure. Residual confounding is very plausible, including depression severity, anxiety, trauma history, socioeconomic strain, product potency, medical versus nonmedical intent, and treatment access. Propensity methods can improve balance on measured variables, but they cannot correct for unmeasured drivers of both cannabis use and suicidality. What This Paper Does Not Show This study does not prove that cannabis directly causes suicidal behaviour in every young adult who uses it. It also does not establish that legalization, cannabis stores, or regulated markets independently increase suicide risk at a population level. How This Fits With the Broader Clinical Conversation Clinical research into Longitudinal Effects of Cannabis Use on Suicidal B is progressing through rigorously documented peer-reviewed cohorts. Evaluating primary evidence enables clinicians to tailor care plans while respecting therapeutic boundaries. Dr. Caplan’s Take *The most clinically useful finding is not that cannabis and suicidal behaviour are linked, since that association has appeared across multiple observational literatures. The more useful detail is that cannabis use at age 25 and increased consumption by age 29 predicted later suicidal behaviour, while previous suicidal behaviour also predicted future suicidal behaviour. In practice, that means cannabis history should not be asked as a yes or no question. Frequency, recent escalation, potency, product type, intoxication pattern, co-use with alcohol or other drugs, and mood context all matter.* *The Washington State and Victoria comparison is especially important because it resists a simple political interpretation. Washington had higher cannabis use in the legal market environment, and proximity to stores was tied to use in propensity analyses, yet Washington did not show higher self-harm at age 29. This suggests that legalization, access, mental health infrastructure, stigma, cultural reporting differences, and baseline population risk may interact in complex ways. Clinicians should translate this into targeted harm reduction: identify high-risk users, screen for suicidality, avoid abrupt moralizing, and coordinate mental health care when cannabis use is increasing.* What a Careful Reader Should Take Away Escalating cannabis use in young adulthood should prompt direct, nonjudgmental screening for depression, self-harm, suicidal thoughts, alcohol use, and other drug use. The study supports clinical vigilance, not blanket fear-based messaging. Evidence Interpretation Guide Table of Contents - [How to Interpret This Clinical Study](#How_to_Interpret_This_Clinical_Study)[Three Rules for Critical Reading](#Three_Rules_for_Critical_Reading) - [CED Perspective Lens: Eight Clinical Viewpoints](#CED_Perspective_Lens_Eight_Clinical_Viewpoints)[Clinical Evidence Synthesis](#Clinical_Evidence_Synthesis) - [Patient Communication](#Patient_Communication) - [Dosing & Formulations](#Dosing_Formulations) - [Safety & Side Effect Profile](#Safety_Side_Effect_Profile) - [Regulatory & Policy Dynamics](#Regulatory_Policy_Dynamics) - [Mechanisms & Physiology](#Mechanisms_Physiology) - [Research Limitations](#Research_Limitations) - [Future Outlook](#Future_Outlook) - [Frequently Asked Questions](#Frequently_Asked_Questions)[Related](#Related) ## How to Interpret This Clinical Study Navigating biomedical publications regarding Longitudinal Effects of Cannabis Use on Suici requires reviewing study methodology and patient eligibility. ### Three Rules for Critical Reading **Separate individual risk from policy conclusions**cannabis use predicted suicidal behaviour, but Washington State did not show higher self-harm at age 29. **Focus on change over time**increasing cannabis use from age 25 to 29 is more clinically informative than a single lifetime-use question. **Look for confounding and vulnerability**prior suicidal behaviour, mental health symptoms, alcohol use, trauma, and social stress may shape both cannabis use and outcomes. Key Evaluation Question Do the models convincingly distinguish cannabis as an independent risk factor from cannabis as a marker of worsening mental health or other substance-related risk? The Patient Question Given my mood history and cannabis pattern, should we screen for suicide risk and consider changing my cannabis use plan? The Bottom Line Young adult cannabis use, especially escalating use, was associated with later suicidal behaviour, but legalization alone did not explain regional self-harm patterns. CED Perspective Lens ## CED Perspective Lens: Eight Clinical Viewpoints Analyzing evidence across clinical, patient, safety, dosing, and physiological perspectives Lens OverviewEight structured clinical perspectives synthesizing primary study data for patient care. #### Clinical Evidence Synthesis This was a longitudinal analysis of 1,470 young adults from the International Youth Development Study, split between Victoria and Washington State. Participants were surveyed around ages 25 and 29, allowing the investigators to assess whether earlier cannabis use and changes in use predicted later suicidal behaviour. The primary signal was consistent: cannabis use at age 25 and increased use by age 29 were associated with increased suicidal behaviour. Prior suicidal behaviour also predicted future suicidal behaviour, which is clinically expected and essential for interpreting risk. Lens takeawayThe strongest clinical signal is escalating use combined with past suicidal behaviour. #### Patient Communication Patients deserve language that is accurate and not alarmist. A useful message is that cannabis use, especially increasing use, may be a warning sign when someone is already struggling with mood, anxiety, trauma, alcohol use, or suicidal thinking. This study supports asking direct questions about self-harm and suicidal thoughts when cannabis use is frequent or rising. It does not support shaming patients, which often reduces honesty and delays help-seeking. Continuous monitoring of real-world outcomes and transparent communication among stakeholders ensures that clinical practice evolves alongside administrative guidelines. Lens takeawayDiscuss risk directly, compassionately, and with attention to changing use patterns. #### Dosing & Formulations The study did not evaluate dose in milligrams, THC potency, CBD content, route of administration, or product formulation. That is a major clinical gap, because daily high-THC inhalation may carry very different risk than intermittent low-dose medical use. For clinical counseling, rising frequency is still meaningful even without product-level data. If a patient reports increasing use, stronger products, wake-and-bake patterns, or use to blunt emotional distress, psychiatric screening becomes more urgent. Continuous monitoring of real-world outcomes and transparent communication among stakeholders ensures that clinical practice evolves alongside administrative guidelines. Lens takeawayFrequency escalation matters clinically, even when precise THC dosing data are absent. #### Safety & Side Effect Profile Suicidal behaviour is not a routine side effect in the way dizziness or dry mouth might be discussed, but it is a critical safety outcome. Cannabis may be part of a broader risk cluster involving depression, impulsivity, sleep disruption, alcohol use, or social stress. The practical safety response is not automatic discontinuation for every patient. It is structured risk assessment, especially when use is increasing, psychiatric symptoms are active, or there is a history of self-harm. Lens takeawayCannabis safety screening should include mood, impulsivity, sleep, and self-harm history. #### Regulatory & Policy Dynamics Washington State had legalized recreational cannabis, while Victoria had not, creating a useful natural policy contrast. Cannabis use was higher and increased over time in Washington, and proximity to cannabis outlets was associated with use in propensity analyses. However, Washington did not show higher self-harm at age 29, which complicates simple legalization narratives. Legal access may increase use, but population suicidal behaviour depends on many determinants beyond cannabis availability. Continuous monitoring of real-world outcomes and transparent communication among stakeholders ensures that clinical practice evolves alongside administrative guidelines. Lens takeawayLegal access may shape cannabis use, but suicidality has broader determinants. #### Mechanisms & Physiology The paper does not test biological mechanisms, but several plausible pathways deserve attention. Heavy THC exposure can affect sleep, anxiety, reward processing, emotional regulation, and cognition, all of which may influence vulnerability in distressed young adults. Another pathway is behavioral rather than purely biological. Cannabis use may increase during periods of worsening mood, social withdrawal, or substance co-use, making it both a possible contributor and a marker of deteriorating mental health. Continuous monitoring of real-world outcomes and transparent communication among stakeholders ensures that clinical practice evolves alongside administrative guidelines. Lens takeawayCannabis may be risk marker, contributor, coping tool, or all three. #### Research Limitations The findings rely on self-report measures, which are vulnerable to recall error and regional differences in willingness to disclose cannabis use or self-harm. The abstract also does not provide detailed effect sizes, confidence intervals, or product characteristics. Observational longitudinal data can strengthen temporal inference but cannot fully remove confounding. Depression severity, trauma exposure, medication treatment, family history, socioeconomic instability, and cannabis potency may all influence the observed relationship. Continuous monitoring of real-world outcomes and transparent communication among stakeholders ensures that clinical practice evolves alongside administrative guidelines. Lens takeawayThe association is clinically meaningful, but causation remains incompletely established. #### Future Outlook Future studies should measure cannabis potency, THC and CBD dose, route, medical versus nonmedical intent, frequency, and cannabis use disorder symptoms. These details would help clinicians distinguish lower-risk patterns from higher-risk escalation. The next step is integrating cannabis assessment into youth and young adult mental health care. Research should also test whether targeted counseling, product changes, reduced use, or treatment of co-occurring depression reduces suicidal behaviour. Continuous monitoring of real-world outcomes and transparent communication among stakeholders ensures that clinical practice evolves alongside administrative guidelines. Lens takeawayBetter product-level data could improve screening, counseling, and harm reduction. Join the Conversation Have a question about how this applies to your situation? [Ask Dr. Caplan](https://benjamincaplan.com/ask-dr-caplan) Want to discuss this topic with other patients and caregivers? [Join the forum discussion](https://cedclinic.com/interact/discussion-forums/forum/cannabis-industry/) [https://cedclinic.com/contact/](https://cedclinic.com/contact/) Physician-Led, Whole-Person Care A doctor who takes the time to truly understand you. Personal care that starts with listening and is guided by experience and ingenuity. Health, Longevity, Wellness One-on-One Cannabis Guidance Metabolic Balance [Leave a Message](https://cedclinic.com/contact/) [Metabolic Care](https://cedclinic.com/metabolic/metabolic-how-it-works/) [Medical Consulting](https://cedclinic.com/book/) [Cannabis Care](https://cedclinic.com/book/) [https://cedclinic.com/contact/](https://cedclinic.com/contact/) Share this Evidence Watch [X](https://twitter.com/intent/tweet?text=Cannabis+Use+and+Suicidal+Behaviour+in+Young+Adults+Across+Washington+State+and+Victoria&url=https%3A%2F%2Fcedclinic.com%2Fced-cannabis-use-and-suicidal-behaviour-2026-09-25%2F) [LinkedIn](https://www.linkedin.com/sharing/share-offsite/?url=https%3A%2F%2Fcedclinic.com%2Fced-cannabis-use-and-suicidal-behaviour-2026-09-25%2F) [BlueSky](https://bsky.app/intent/compose?text=Cannabis+Use+and+Suicidal+Behaviour+in+Young+Adults+Across+Washington+State+and+Victoria%20https%3A%2F%2Fcedclinic.com%2Fced-cannabis-use-and-suicidal-behaviour-2026-09-25%2F) [Instagram](https://www.instagram.com/drcaplan/) [Substack](https://doctorapprovedcannabis.substack.com/) [RSS](https://cedclinic.com/feed/) Source: [Primary Source: Longitudinal Effects of Cannabis Use on Suicidal Behaviour in Early Adulthood in Washington State, United States and Victoria, Australia.](https://pubmed.ncbi.nlm.nih.gov/42782471/) Related Reading at CED ClinicContinue exploring the evidence[Prenatal Cannabis Exposure and Neurodevelopment: What the New Systematic Review Actually Shows](https://cedclinic.com/prenatal-cannabis-neurodevelopment-impact/) More on this topic: Systematic review analyzing cognitive, behavioral, and developmental trajectories following gestational cannabinoid exposure. [More on this topic: Fetal neurodevelopment](https://cedclinic.com/prenatal-cannabis-neurodevelopment-impact/)[Adolescent Cannabis Use and Its Impact on Cognitive Development: Insights from the ABCD Study](https://cedclinic.com/adolescent-cannabis-use-cognitive-development-risk/) More on this topic: Long-term ABCD study findings on adolescent brain development, executive function, and early cannabis susceptibility. [More on this topic: Adolescent brain health](https://cedclinic.com/adolescent-cannabis-use-cognitive-development-risk/)[The Multifaceted Impact of CBD on Sleep: A Comprehensive Guide for Better Rest](https://cedclinic.com/the-multifaceted-impact-of-cbd-on-sleep-a-comprehensive-guide-for-better-rest/) More on this topic: Clinical insights into sleep architecture, circadian rhythm modulation, and cannabinoid titration for insomnia. [More on this topic: Cannabinoids & sleep](https://cedclinic.com/the-multifaceted-impact-of-cbd-on-sleep-a-comprehensive-guide-for-better-rest/) ## Frequently Asked Questions Did this study prove that cannabis causes suicide? No. It found that cannabis use and increasing use were associated with later suicidal behaviour, but the observational design cannot prove direct causation for every patient. Who was studied? The study followed 1,470 young adults from the International Youth Development Study, including 726 participants from Victoria, Australia and 744 from Washington State, United States. At what ages were participants assessed? Participants were surveyed at average ages of about 25 in 2014 and 29 in 2018, allowing researchers to evaluate changes over early adulthood. What cannabis pattern seemed most concerning? Higher cannabis use at age 25 and increased cannabis consumption by age 29 predicted increased suicidal behaviour. Clinically, escalation over time is especially important. Did legalization explain higher suicidal behaviour? Not by itself. Washington State had legal recreational cannabis and higher cannabis use, but it also had lower self-harm at age 29 than Victoria. Should young adults with depression avoid cannabis? They should discuss cannabis use with a clinician, especially if use is frequent, increasing, high in THC, or used to manage distress. Depression and suicidal thoughts require direct clinical attention. Does CBD have the same risk as THC? This study did not separate THC from CBD or analyze product formulations. Therefore, it cannot determine whether CBD-dominant products carry the same, lower, or different risk. What should clinicians ask patients based on this study? Clinicians should ask about cannabis frequency, recent escalation, potency, route, alcohol and drug co-use, mood symptoms, sleep, self-harm history, and current suicidal thoughts. Does proximity to cannabis stores matter? Propensity analysis suggested legalization indicators, including Washington State location and proximity to cannabis outlets, were associated with cannabis use. That does not prove stores independently cause suicidal behaviour. What should a patient do if cannabis use is increasing and mood is worsening? They should contact a healthcare professional promptly, especially if self-harm thoughts are present. If there is imminent danger, emergency services or a crisis hotline should be used immediately. ### Related --- ### Verification & Medical Governance - **Lead Clinical Author:** Benjamin Caplan, MD - **Credentials:** Board Certified in Family Medicine (ABFM), Former CMO Canna Care Docs (250,000+ patients supervised), Founder & CMO CED Clinic & CED Foundation, Author of *The Doctor-Approved Cannabis Handbook* (Penguin Random House). - **Clinical Scale:** 350,000+ lifetime evaluations overseen; 81,008-patient Real-World Evidence Registry (`~/.ced_rwe_vault.db`); 125,000+ peer-reviewed study literature observatory (`http://localhost:8768/api/explorer/terminal`). - **License Verification:** Commonwealth of Massachusetts License #240562 (https://checkahealthlicense.mass.gov/). - **NPI Registry:** 1962722637 (https://npiregistry.cms.hhs.gov/provider-view/1962722637). - **Ethics & Data Privacy:** Clinical registry observations adhere strictly to HIPAA Safe Harbor de-identification (45 CFR § 164.514(b)) and criteria for secondary research exemption under 45 CFR § 46.104(d)(4).