Key Takeaways
- The strongest evidence for benefit comes from purified CBD, which significantly reduces seizures in hard-to-treat epilepsies like Dravet and Lennox-Gastaut syndromes.
- For chronic pain, certain high-THC to CBD ratio products deliver small but real improvements in pain and function, though many patients experience side effects and benefits are modest.
- Medicinal cannabis often improves quality of life in people with serious chronic conditions, including better sleep, mood, and reduced reliance on opioids.
- High-potency THC cannabis (especially daily use) raises the risk of psychosis and schizophrenia 3–5 times, with the strongest signals in adolescents and young adults.
- Cannabis use in teens is linked to slower development in memory, executive function, and processing speed, even after accounting for family background and other factors.
- Regular cannabis use is associated with higher risks of heart attack, stroke, and cardiovascular death, independent of tobacco use.
Cannabis: Good or Bad?
Marijuana is no longer a fringe topic. With legalization in dozens of states and countries, more people are using it daily than alcohol in some places. Supporters talk about relief from chronic pain, epilepsy, anxiety, and the stress of serious illness. Critics point to today’s much stronger products, rising emergency-room visits for psychosis, concerns about teen brain development, and new data on heart risks.
The science is complicated because cannabis is not one substance. It contains over 100 cannabinoids, with THC driving the high and most risks, while CBD is non-intoxicating and often helpful. Studies also mix smoked flower, vapes, edibles, oils, and pharmaceutical-grade products. Age of first use, frequency, potency, and genetics all matter enormously.
This article examines six major recent studies and reviews (2024–2025) that together paint the clearest picture available. For each, we look at what the research actually found, how it was done, what it does and doesn’t prove, and how it fits with the rest of the evidence. The goal is straightforward: give you the facts so you can decide for yourself.
Chronic Pain: Small Improvements, Real Trade-offs
The most comprehensive look at cannabis for pain is the 2025 living systematic review from the Agency for Healthcare Research and Quality (Chou et al., Annals of Internal Medicine). This update added new trials and now includes 29 randomized controlled trials and 15 observational studies.
High-THC to CBD ratio products (like certain oral sprays) produced small reductions in pain severity—about half to one point on a 0–10 scale—and modest gains in physical function compared with placebo. Synthetic or purified high-THC options showed similar small pain relief but came with more dizziness, sedation, and nausea. Low-THC or CBD-dominant products usually performed no better than placebo.
In real-world observational data, many patients reported sustained improvements over months, including less opioid use and better sleep. However, dropout rates were high in trials because of side effects, and long-term data beyond a year remain limited.
What the Study Really Found
The review graded the evidence as moderate for small pain and function benefits from certain THC-dominant products, and low to moderate for increased side effects. Importantly, it found no strong evidence that cannabis eliminates pain or works better than standard treatments for most people.
Strengths, Limitations, and What It Means in Practice
Strengths include the sheer volume of data and careful separation of product types. Limitations are the short duration of most trials and the fact that many participants knew they were getting cannabis (expectation bias). In practice, this means cannabis can be a helpful add-on for some chronic pain patients, especially those who haven’t responded well to other treatments, but it is rarely a game-changer on its own.
Epilepsy: One of the Clear Success Stories
A 2024 network meta-analysis in Frontiers in Neurology compared different doses of oral CBD for refractory epilepsies. CBD at 20 mg/kg/day came out on top for reducing seizures by at least 50% (relative risk 1.91 versus placebo) and for achieving seizure freedom. Higher doses gave similar seizure control but more side effects; lower doses were less effective.
This aligns with the FDA-approved drug Epidiolex, which is purified CBD and has transformed care for these severe childhood epilepsies where other drugs often fail.
What the Study Really Found
CBD works through multiple mechanisms, including modulating neuronal excitability and reducing inflammation in the brain. The analysis showed clear dose-response patterns and benefits that held across different epilepsy syndromes.
Strengths, Limitations, and What It Means in Practice
The network design let researchers compare doses indirectly, and seizure counts were objective (parent diaries plus EEG in many cases). The main drawbacks are the relatively short trial lengths (12–16 weeks) and common side effects like sleepiness and diarrhea. For families dealing with frequent, dangerous seizures, CBD is often life-changing. For other types of epilepsy, the evidence is much weaker.
Quality of Life: Real Gains for People with Serious Illness
A 2025 systematic review and meta-analysis of 64 studies (mostly 2015–2025) looked at health-related quality of life in patients using medicinal cannabis (published in Quality of Life Research). Across chronic pain, cancer, multiple sclerosis, and other conditions, small-to-moderate improvements appeared in pain, sleep, mood, and daily functioning within the first three months, and these gains often lasted 6–12 months or longer in observational follow-up.
Many patients also reported cutting back on opioids and benzodiazepines.
What the Study Really Found
Improvements were most consistent in people using cannabis for approved medical reasons under supervision. The effect sizes were modest but meaningful for people living with debilitating conditions.
Strengths, Limitations, and What It Means in Practice
The review included both trials and real-world data, giving a fuller picture than RCTs alone. The biggest limitation is that people who seek out medical cannabis may already be more motivated or have different baselines than those who don’t. Still, the pattern suggests cannabis can meaningfully improve daily life for some patients when other options fall short.
Psychosis: The Strongest and Most Consistent Risk
A meta-analysis in Nature Mental Health and related CMAJ data confirmed that high-potency cannabis (over 10–15% THC) and daily use are strongly linked to psychosis. Daily high-potency users had approximately 3–5 times higher odds of psychotic disorders compared with non-users. In certain European cities where high-potency cannabis dominates the market, modeling studies estimate that a substantial proportion of first-episode psychosis cases may be attributable to heavy cannabis use. These estimates vary by region and assume a causal relationship, which is strongly supported but not definitively proven in every case.
One large registry-based study found that individuals diagnosed with cannabis-induced psychotic disorder had a dramatically higher relative risk of later being diagnosed with schizophrenia compared with the general population. However, this estimate reflects a high-risk subgroup already experiencing severe psychiatric symptoms and does not mean that most cannabis users will develop schizophrenia. Absolute risk remains far lower than the relative figure suggests, and genetic vulnerability and other psychiatric risk factors play a major role.
What the Study Really Found
The risk is dose-dependent and much higher with modern high-THC products than with the weaker cannabis of the 1990s. Genetic vulnerability (certain COMT and AKT1 variants) and early age of use amplify the danger.
Strengths, Limitations, and What It Means in Practice
The analysis drew from large international cohorts and experimental THC challenge studies, making the case unusually robust. Reverse causation remains possible in some observational data, but the overall evidence is now hard to dismiss. For young people and those with family history of psychosis, heavy use is playing with fire.
Adolescent Brain Development: Poorer Neurocognitive Performance
Data from the Adolescent Brain Cognitive Development (ABCD) Study—one of the largest and most diverse U.S. youth cohorts (n > 11,000)—show that cannabis use during early-to-mid adolescence associates with poorer performance on key cognitive tasks. Hair toxicology provides objective confirmation of exposure (detecting THC metabolites like THCCOOH over ~3 months), reducing reliance on self-report bias.
What the Study Really Found
In analyses at ages 13–14 (Year 4 follow-up), youth with hair-confirmed cannabis use (THC/THCCOOH present) scored lower on episodic memory tasks (e.g., Picture Memory) compared with matched non-using controls. Within users, higher hair THCCOOH levels correlated with poorer performance on verbal reasoning (Picture Vocabulary), inhibitory control/attention (Flanker task), and working memory (List Sorting). Past-year self-reported use also negatively associated with List Sorting Working Memory and Picture Sequence Memory. These associations held after matching on confounders like socioeconomic status, family environment, and other substance use.
Strengths, Limitations, and What It Means in Practice
Strengths: ABCD offers repeated assessments, standardized NIH Toolbox cognitive batteries, and multi-modal substance verification (hair, urine, self-report). Hair toxicology improves accuracy by capturing moderate-to-heavy chronic use objectively.
Limitations: This analysis is cross-sectional (ages 13–14), so it shows associations at a snapshot rather than long-term change over time. The cohort is still mid-adolescence (full adult follow-up ongoing), and some residual confounding can’t be ruled out entirely.
In practice: These findings highlight adolescence as a sensitive period—the developing prefrontal cortex and hippocampal systems (critical for memory and executive control) appear particularly vulnerable to THC’s effects. For parents, educators, and teens, the evidence supports delaying or avoiding cannabis use to protect cognitive development. Ongoing ABCD follow-up will clarify if these deficits persist or worsen into adulthood.
Cardiovascular Risks: A Growing Concern
A 2025 systematic review and meta-analysis published in Heart synthesized 24 real-world pharmacoepidemiological studies (17 cross-sectional, 6 cohort, 1 case-control) to assess cannabis/cannabinoid use and major adverse cardiovascular events (MACE), including cardiovascular death, non-fatal acute coronary syndrome (ACS, encompassing myocardial infarction), and non-fatal stroke (Storck et al., 2025). All studies focused on cannabis exposure (one on medical cannabis), with data spanning 2016–2023 and involving millions of participants across multiple countries.
What the Study Really Found
Pooled adjusted risk ratios (RRs) showed positive associations:
- Acute coronary syndrome (ACS): RR 1.29 (95% CI 1.05 to 1.59)
- Stroke: RR 1.20 (95% CI 1.13 to 1.26)
- Cardiovascular death: RR 2.10 (95% CI 1.29 to 3.42)
A composite ACS/stroke outcome (from two studies) showed no significant association. Restricting to cohort studies alone yielded similar results (e.g., ACS RR 1.32, 95% CI 1.01 to 1.73). Risks persisted after adjustments for tobacco use and other confounders in included studies, and increased with greater frequency/exposure in patterns observed across the data.
Mechanisms
THC acutely increases heart rate (tachycardia), blood pressure (via sympathetic activation), and can provoke coronary vasospasm, arrhythmias, or demand ischemia—particularly in vulnerable individuals. Chronic use may contribute to endothelial dysfunction, inflammation, and pro-thrombotic states. These effects are more pronounced in older adults or those with preexisting cardiovascular disease/risk factors (e.g., hypertension, diabetes), though signals appear even in younger, otherwise healthy users.
Strengths, Limitations, and What It Means in Practice
Strengths: Real-world focus on adjusted estimates from large observational datasets; use of ROBINS-E for quality assessment; DerSimonian-Laird random-effects pooling for heterogeneity.
Limitations: High heterogeneity (I² often substantial to considerable across outcomes); reliance on self-reported exposure in many studies (potential misclassification); mostly observational design (cannot prove causation—residual confounding possible despite adjustments); limited data on specific routes (smoking vs. edibles vs. vaping), potency, or medical vs. recreational use; search limited to 2016–2023 (misses newer high-potency trends).
In practice: Absolute risks remain low for young, healthy, infrequent users, but relative increases matter for vulnerable groups—older adults, those with heart disease history, or frequent users. Clinicians should routinely screen for cannabis use in patients with cardiovascular symptoms or risk factors, similar to tobacco. The consistent signal across real-world data underscores caution, especially as daily/high-potency use rises. More prospective studies on modern consumption patterns are needed to clarify dose-response and mechanisms.
Why the Contradictions Exist
Cannabis is a complex plant whose effects depend on which compounds dominate, how it’s consumed, who is using it, and how often. Low-dose CBD is often beneficial; high-dose THC daily in a teenage brain is often harmful. Medical studies usually test controlled products in sick patients; recreational studies capture heavy, high-potency use in healthy young people. Genetics, co-use with tobacco or alcohol, and socioeconomic factors explain a lot of the variation.
Related Reading:
Cannabis Use May Alter Midbrain Dopamine Activity and Elevate Psychosis Risk
High-Potency Cannabis Linked to Greater Addiction, Psychosis Risk: What to Know
Brain Stimulation Shows Promise for Cannabis Use Disorder in People with Schizophrenia
The Beneficial Effects of Cannabis on Post-Traumatic Stress Disorder Are Short Lived
Abusing Cannabis Increases the Risk of Testicular Cancer
Proven Strategies for Successful Smoking Cessation: A Science-Backed Guide
FAQs: Marijuana and Your Health
Is marijuana addictive?
Yes. Approximately 9–30% of people who use cannabis develop cannabis use disorder. The risk is significantly higher among those who begin using during adolescence and among people who use high-THC products daily.
Does CBD make you high?
No. Cannabidiol (CBD) is non-intoxicating. The psychoactive “high” associated with marijuana comes from tetrahydrocannabinol (THC).
Which is safer: smoking, vaping, or edibles?
Edibles and tinctures are generally safer for the lungs because they avoid combustion. Vaping may expose users to fewer toxins than smoking, but it still carries risks related to heating devices and additives. Smoking is associated with the greatest long-term lung irritation and airway damage.
Can marijuana help anxiety and depression?
Some people experience short-term relief from anxiety with low doses of balanced THC and CBD products. However, frequent or high-THC use is associated with worsening anxiety, panic symptoms, and depression over time. Effects vary by individual.
Is marijuana safe during pregnancy?
No. Cannabis use during pregnancy is strongly discouraged. Research links prenatal exposure to lower birth weight, preterm birth, smaller head circumference, and later attention and behavioral problems in children.
Does marijuana permanently damage the brain?
Heavy use during adolescence is associated with lasting changes in memory, learning, and executive function. Occasional adult use shows little evidence of permanent structural damage, but long-term data are still evolving.
Are concentrates (dabs, wax, shatter) more dangerous?
Yes. Concentrates contain very high THC levels and are associated with greater risks of psychosis, severe anxiety, panic reactions, addiction, and cannabinoid hyperemesis syndrome.
Can you drive after using marijuana?
No. Cannabis impairs reaction time, attention, coordination, and decision-making. Impairment may last 4–10 hours or longer, especially with edibles.
Does marijuana help with sleep?
Short term, many people fall asleep faster. Long term, regular use may reduce REM sleep, lead to tolerance, and cause rebound insomnia when stopped.
Is marijuana a gateway drug?
Current evidence does not strongly support the idea that cannabis directly causes progression to harder drugs. Shared risk factors such as genetics, trauma, and environmental influences likely explain much of the association.
What is cannabinoid hyperemesis syndrome (CHS)?
CHS is a condition characterized by repeated cycles of severe vomiting in people who use cannabis heavily over long periods. Symptoms typically resolve only with complete cessation. Hot showers may provide temporary relief.
Does marijuana affect testosterone or fertility?
Heavy or frequent use may temporarily lower testosterone levels and reduce sperm count and motility. These effects are usually reversible after several weeks to months of abstinence.
Is medical marijuana safer than recreational products?
Medical products are typically regulated for potency and contaminants and are used under clinician supervision, which generally improves safety compared with unregulated use.
Can marijuana replace opioids for chronic pain?
Cannabis does not eliminate chronic pain for most people. However, some patients are able to reduce their opioid dosage when cannabis is added to their treatment plan. Pain relief is usually modest.
Does smoking marijuana cause lung cancer?
Current evidence suggests a much weaker association with lung cancer than tobacco. However, smoking cannabis can cause chronic bronchitis, cough, airway inflammation, and lung irritation.
Is secondhand marijuana smoke harmful?
Yes. Secondhand cannabis smoke contains many of the same toxic chemicals found in tobacco smoke and may be particularly harmful for children and individuals with respiratory conditions.
What is the safest way to consume cannabis?
While no method is risk-free, general consensus suggests the following order from lower to higher respiratory risk:
- Tinctures or oils (sublingual)
- Low-dose edibles
- Vaporized dry herb
- Vaporized concentrates
- Smoking or dabbing
Even lower-risk methods may carry cardiovascular, cognitive, or psychiatric risks depending on dose and frequency.
Does marijuana interact with medications?
Yes. Cannabis may interact with blood thinners, sedatives, antidepressants, anti-anxiety medications, and certain anti-epileptic drugs. Always inform your healthcare provider if you use cannabis.
Did teen marijuana use increase after legalization?
The evidence is mixed. In most regions, adolescent use did not dramatically increase after legalization. Adult use increased more consistently.
How long does THC stay in the body?
Detection times vary by frequency of use:
- Single use: typically 2–7 days in urine
- Regular moderate use: approximately 1–3 weeks
- Daily or heavy use: 4–8 weeks or longer
- Hair testing: up to 90 days
Does marijuana increase the risk of heart attack or stroke?
Emerging evidence suggests cannabis use is associated with approximately 25–30% higher relative risk of acute coronary events and about 20% higher stroke risk. Risk appears greater with frequent use and in older adults.
Can you overdose and die from marijuana?
Fatal overdose from THC alone is extremely rare. However, very high doses—particularly from edibles—can cause severe anxiety, vomiting, psychosis-like symptoms, and, in rare cases, serious cardiac rhythm disturbances.
Is marijuana stronger now than in the 1990s?
Yes. Average THC levels in cannabis flower were around 3–5% in the 1990s. Today, 15–30% THC is common, and concentrates may exceed 60–90%.
Does marijuana cause “amotivational syndrome”?
Heavy, chronic use is associated with reduced motivation and poorer life outcomes. However, it remains difficult to determine whether cannabis directly causes these effects or whether underlying factors contribute to both.
Bottom line — should I use marijuana?
General risk guidance:
- Under age 25: Avoid if possible due to brain development risks
- Pregnant or planning pregnancy: Avoid completely
- Personal or family history of psychosis: High risk — avoid
- Healthy adult using occasionally, low-potency, non-smoked forms: Lower relative risk
- Daily, high-potency, or early initiation: Substantially higher risk
Individual risk varies. Discuss personal circumstances with a healthcare professional.
Final Thoughts
Marijuana sits in a nuanced space: it offers real medical value in specific cases while carrying meaningful risks in others. Purified CBD stands out with strong evidence for reducing seizures in severe, treatment-resistant epilepsies like Dravet and Lennox-Gastaut syndromes. For chronic pain and certain serious illnesses, THC-dominant cannabis medicines can deliver modest relief—small reductions in pain intensity and improvements in sleep, mood, and daily function—often helping patients cut back on opioids or other drugs. These benefits are most reliable when use is medically supervised with standardized products.
On the risk side, the data are sobering. High-potency THC (common today at 15–30%+) and frequent use are strongly linked to psychosis, with daily heavy users facing 3–5 times higher odds of psychotic disorders—especially alarming for adolescents and young adults whose developing brains show poorer performance in memory, executive control, and processing speed. Emerging cardiovascular signals are concerning too: cannabis use associates with roughly 29% higher acute coronary syndrome risk, 20% higher stroke risk, and more than double the risk of cardiovascular death, even after tobacco adjustment. Absolute risks stay low for young, healthy, infrequent users, but they climb meaningfully for older adults or those with heart risk factors.
The divide in the literature largely reflects exposure differences: controlled medical trials show benefits with manageable side effects, while real-world heavy recreational use drives the harms. Age, potency, frequency, genetics, and co-use with tobacco or alcohol explain most of the variation.
In short:
- For healthy adults over 25 using occasionally, low-potency, non-smoked products, risks are generally low and manageable.
- For teens, young adults, pregnant people, or anyone with mental health or heart concerns, avoidance is the safest path; medical use should only occur under close physician oversight.
Legalization for adults does not mean harmlessness—treat cannabis like alcohol. Smart regulation (potency limits, age enforcement, clear labeling, ongoing research) and personal decisions informed by current evidence, not hype, are the way forward. When in doubt, talk to a doctor.
References
Chou R, et al. (2025). Cannabis-based products for chronic pain: An updated systematic review. Annals of Internal Medicine. https://doi.org/10.7326/ANNALS-25-03152
Wang, X., Zhu, H., Liu, T., Guo, Z., Zhao, C., He, Z., & Zheng, W. (2024). Comparison of various doses of oral cannabidiol for treating refractory epilepsy indications: A network meta-analysis. Frontiers in Neurology, 15, Article 1243597. https://doi.org/10.3389/fneur.2024.1243597
Tait, M. A., Acret, L., Costa, D. S. J., Campbell, R., White, K., & Rutherford, C. (2026). Health-related quality of life in patients receiving medicinal cannabis: Systematic review and meta-analysis of primary research findings 2015–2025. Quality of Life Research, 35(3), 56. https://doi.org/10.1007/s11136-026-04170-7
Schoeler, T., Baldwin, J.R., Martin, E. et al. Assessing rates and predictors of cannabis-associated psychotic symptoms across observational, experimental and medical research. Nat. Mental Health 2, 865–876 (2024). https://doi.org/10.1038/s44220-024-00261-x
Wade, N. E., Wallace, A. L., Huestis, M. A., Lisdahl, K. M., Sullivan, R. M., & Tapert, S. F. (2024). Cannabis use and neurocognitive performance at 13–14 Years-Old: Optimizing assessment with hair toxicology in the Adolescent brain cognitive development (ABCD) study. Addictive Behaviors, 150, 107930. https://doi.org/10.1016/j.addbeh.2023.107930
Storck, W., Elbaz, M., Vindis, C., Déguilhem, A., Lapeyre-Mestre, M., & Jouanjus, E. (2025). Cardiovascular risk associated with the use of cannabis and cannabinoids: A systematic review and meta-analysis. Heart, 111(22), 1047–1056. https://doi.org/10.1136/heartjnl-2024-325429
