Cannabis and Cannabinoids (Marijuana)

Safety and precautions

We advise medical supervision and monitoring when using cannabis for medical purposes. Cannabis can cause upsetting experiences for some people, including psychosis, distress, anxiety, and sedation.

The proportions of THC and CBD in cannabis can vary widely from one product to another, and the proportion of THC has increased considerably in the last few decades in some varieties.¹Hilzenrath D. Legal pot is more potent than ever—and still largely unregulated. KFF Health News. May 9, 2023. Viewed May 18, 2023. More potent products may be contributing to a large number of visits to emergency departments for cannabis-related issues—more than 800,000 in the US in 2021.²Drug Abuse Warning Network (DAWN). Findings from Drug-Related Emergency Department Visits, 2021. US Department of Health and Human Services Substance Abuse and Mental Health Services Administration. December 2022. 

Cannabis also impairs driving and other tasks requiring judgment and rapid response. Caution is warranted.

Cancer risk

Cannabis use is linked to higher risk of some types of cancer.

Side effects or adverse events

Cardiovascular health effects

Smoking cannabis carries many of the same cardiovascular health hazards as smoking tobacco.¹⁰DeFilippis EM, Bajaj NS et al. Marijuana use in patients with cardiovascular disease: JACC Review Topic of the Week. Journal of the American College of Cardiology. 2020 Jan 28; 75(3):320-332; American College of Cardiology. Potential link between marijuana and heart risks discovered by cardiologists. SciTechDaily. January 20, 2020. Viewed October 9, 2021. Whether cannabis-based edibles also cause these hazards is unclear because many large studies do not separate participants based on whether they smoked or ate cannabis. However both CBD and THC can cause inflammation, oxidative stress, and cell damage in the cardiovascular system.¹¹Pacher P, Steffens S et al. Cardiovascular effects of marijuana and synthetic cannabinoids: the good, the bad, and the ugly. Nature Reviews. Cardiology. 2018 Mar;15(3):151-166; Page RL 2nd, Allen LA et al. Medical marijuana, recreational cannabis, and cardiovascular health: a scientific statement from the American Heart Association. Circulation. 2020 Sep;142(10): e131–e152. A 2025 analysis of 24 studies (mostly very large cohort studies) found that people who used cannabis had an increased risk of cardiovascular disorders, but the rate of stroke or heart attack was very low.¹²Storck W, Elbaz M et al. Cardiovascular risk associated with the use of cannabis and cannabinoids: a systematic review and meta-analysis. Heart. 2025 Jun 17:heartjnl-2024-325429. 

Gastrointestinal symptoms

Although cannabis can be helpful for nausea in some people, there is also modest evidencesignificant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observational studies), or several small studies aggregated into a meta-analysis (this is the CancerChoices definition; other researchers and studies may define this differently) of a higher risk of nausea and vomiting among people treated with oral cannabis:

• Slightly higher risk of nausea and vomiting among people with chronic pain or cancer treated with oral cannabis compared to placebo in a combined analysis of 32 RCTsrandomized controlled trial, a study design in which people are randomly assigned to either an experimental group or a control group to compare the outcomes from different treatments; an RCT is considered a strong design for determining a therapy’s effects¹³Wang L, Hong PJ et al. Medical cannabis or cannabinoids for chronic non-cancer and cancer related pain: a systematic review and meta-analysis of randomised clinical trials. BMJ. 2021 Sep 8;374:n1034.
• Higher risk of nausea and vomiting but no evidence of an effect on constipation among people with chronic cancer pain when adding cannabis to prescription opioids compared to opioids alone in a meta-analysisa statistical analysis that combines the results of two or more research studies; the results of smaller research studies addressing the same or similar questions can be analyzed as though they are one bigger, more powerful study of 5 RCTs¹⁴Noori A, Miroshnychenko A et al. Opioid-sparing effects of medical cannabis or cannabinoids for chronic pain: a systematic review and meta-analysis of randomised and observational studies. BMJ Open. 2021 Jul 28;11(7):e047717.

Liver damage

There is good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) that cannabis treatment can cause elevated liver enzymes in some people.¹⁵Lo LA, Christiansen A et al. Cannabidiol-associated hepatotoxicity: A systematic review and meta-analysis. Journal of Internal Medicine. 2023 Jun;293(6):724-752.

Neurological side effects

There is good evidence that cannabis can cause euphoria; a feeling of being high; and sedation (drowsiness).¹⁶Rabgay K, Waranuch N et al. The effects of cannabis, cannabinoids, and their administration routes on pain control efficacy and safety: a systematic review and network meta-analysis. Journal of the American Pharmacists Association. 2020 Jan-Feb;60(1):225-234.e6; Smith LA, Azariah F, Lavender VT, Stoner NS, Bettiol S. Cannabinoids for nausea and vomiting in adults with cancer receiving chemotherapy. Cochrane Database of Systematic Reviews. 2015 Nov 12;2015(11):CD009464; Wang L, Hong PJ et al. Medical cannabis or cannabinoids for chronic non-cancer and cancer related pain: a systematic review and meta-analysis of randomised clinical trials. BMJ. 2021 Sep 8;374:n1034. There is also good evidence that taking cannabis can cause short-term cognitive impairment among people with cancer.¹⁷Wang L, Hong PJ et al. Medical cannabis or cannabinoids for chronic non-cancer and cancer related pain: a systematic review and meta-analysis of randomised clinical trials. BMJ. 2021 Sep 8;374:n1034.

There is modest evidence of more dysphoria (low mood) among people taking cannabis to help with chemotherapy-induced nausea and vomiting than those taking conventional treatments or placebos.¹⁸Smith LA, Azariah F, Lavender VT, Stoner NS, Bettiol S. Cannabinoids for nausea and vomiting in adults with cancer receiving chemotherapy. Cochrane Database of Systematic Reviews. 2015 Nov 12;2015(11):CD009464; Chow R, Valdez C et al. Oral cannabinoid for the prophylaxis of chemotherapy-induced nausea and vomiting—a systematic review and meta-analysis. Supportive Care in Cancer. 2020;28:2095-2103.

There is good evidence that some people taking cannabis for cancer-related pain and nausea experience dizziness.¹⁹Wang L, Hong PJ et al. Medical cannabis or cannabinoids for chronic non-cancer and cancer related pain: a systematic review and meta-analysis of randomised clinical trials. BMJ. 2021 Sep 8;374:n1034; Whiting PF, Wolff RF et al. Cannabinoids for medical use: a systematic review and meta-analysis. JAMA. 2015 Jun 23-30;313(24):2456-73; McDonagh MS, Morasco BJ et al. Cannabis-based products for chronic pain: a systematic review. Annals of Internal Medicine. 2022 Jun 7; Grimison P, Mersiades A et al. Oral THC:CBD cannabis extract for refractory chemotherapy-induced nausea and vomiting: a randomised, placebo-controlled, phase II crossover trial. Annals of Oncology. 2020;31:1553-1560.  

Among people with cancer and no mental illness, a large combined analysis of studies did not find evidence that cannabis led to more hallucinations or psychosis.²⁰Grimison P, Mersiades A et al. Oral THC:CBD cannabis extract for refractory chemotherapy-induced nausea and vomiting: a randomised, placebo-controlled, phase II crossover trial. Annals of Oncology. 2020;31:1553-1560; Mücke M, Carter C et al. Cannabinoide in der palliativen Versorgung: Systematische Übersicht und Metaanalyse der Wirksamkeit, Verträglichkeit und Sicherheit [Cannabinoids in palliative care: systematic review and meta-analysis of efficacy, tolerability and safety]. Schmerz. 2016 Feb;30(1):25-36. German; Mücke M, Weier M. Systematic review and meta-analysis of cannabinoids in palliative medicine. Journal of Cachexia, Sarcopenia and Muscle. 2018 Apr;9(2):220-234. However, wider analyses (not limited to people with cancer) have found a greater risk of mental illness onset among people who use cannabis.²¹Hasan A, von Keller R et al. Cannabis use and psychosis: a review of reviews. European Archives of Psychiatry and Clinical Neuroscience. 2020 Jun;270(4):403-412. People with advanced cancer who experienced pain relief from cannabis also experienced more neurological toxicity (a higher risk of hallucinations and paranoia) in a mid-sized RCT.²²Hardy JR, Greer RM et al. Medicinal cannabis for symptom control in advanced cancer: a double-blind, placebo-controlled, randomised clinical trial of 1:1 tetrahydrocannabinol and cannabidiol. Support Care Cancer. 2025 Jul 24;33(8):715.

Importantly, there is strong evidenceconsistent, significant effects in several large (or at least one very large) well designed clinical studies or at least two meta-analyses of clinical studies of moderate or better quality (or one large meta-analysis) finding similar results (this is the CancerChoices definition; other researchers and studies may define this differently) that using cannabis—especially high-potency THC products—can induce relapse among people who already experience psychosis or hallucinations.²³Hasan A, von Keller R et al. Cannabis use and psychosis: a review of reviews. European Archives of Psychiatry and Clinical Neuroscience. 2020 Jun;270(4):403-412; Petrilli K, Ofori S et al. Association of cannabis potency with mental ill health and addiction: a systematic review. Lancet Psychiatry. 2022 Jul 25:S2215-0366(22)00161-4.

Oral tissue damage

There is preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) that smoking cannabis damages the tissues that surround and support the teeth (periodontium) among people who smoke cannabis.²⁴Keboa MT, Enriquez N, Martel M, Nicolau B, Macdonald ME. Oral health implications of cannabis smoking: a rapid evidence review. Journal of the Canadian Dental Association. 2020 Jan;86:k2.

Worse outcomes in pregnancy

Strong evidence of worse outcomes for pregnant people and infants: A large combined analysis of studies found that people who used cannabis during pregnancy had a higher risk of high blood pressure, but a lower risk of gestational diabetes. The babies in this analysis had a higher risk of several negative outcomes, but according to a more recent review by an expert committee, the current evidence only supports a risk of low birth rate with cannabis use.²⁵Sainz K, Ulibarri H et al. Meta-analysis of maternal and neonatal outcomes of cannabis use in pregnancy current to March 2024. Maternal Health, Neonatology, and Perinatology. 2025 Aug; National Academies of Sciences, Engineering, and Medicine; Health and Medicine Division; Board on Population Health and Public Health Practice; Committee on the Health Effects of Marijuana: An Evidence Review and Research Agenda. The Health Effects of Cannabis and Cannabinoids: The Current State of Evidence and Recommendations for Research. Washington (DC): National Academies Press (US); 2017 Jan 12; correspondence with Dr. Donald Abrams

Side effects as a whole

There was modest evidencesignificant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observational studies), or several small studies aggregated into a meta-analysis (this is the CancerChoices definition; other researchers and studies may define this differently) of adverse side effects (chiefly drowsiness and dizziness) with very high doses of THC.²⁶McDonagh MS, Morasco BJ et al. Cannabis-based products for chronic pain: a systematic review. Annals of Internal Medicine. 2022 Jun 7. There were also more side effects among people treated with cannabis for chemotherapy-induced nausea and vomiting compared to conventional antinausea medications.²⁷Tafelski S, Häuser W, Schäfer M. Efficacy, tolerability, and safety of cannabinoids for chemotherapy-induced nausea and vomiting—a systematic review of systematic reviews. Schmerz. 2016;30:14-24.

Interactions with cancer treatments

People with cancer using cannabis had worse outcomes on immunotherapy in two studies
(preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently)), though another study did not find this effect.

• Substantially shorter time to tumor progression and overall survival, and a worse marker of immune function (lymphocyte count) among people with advanced cancer initiating immunotherapy using cannabis in a mid-sized observationala type of study in which individuals are observed or certain outcomes are measured, but no attempt is made to affect the outcome (for example, no treatment is given); an example is a study that records people’s diets, but doesn’t try to alter their diets, and looks for patterns of disease or other outcomes related to different foods study²⁸Bar-Sela G, Cohen I et al. Cannabis consumption used by cancer patients during immunotherapy correlates with poor clinical outcome. Cancers (Basel). 2020 Aug 28;12(9):2447.  
• Substantially lower response to immunotherapy (nivolumab), but no evidence of an effect on progression-free or overall survival, among people with advanced cancers—melanoma, non-small cell lung cancer, or renal clear cell carcinoma—using cannabis compared to no cannabis in a mid-sized observational study²⁹Taha T, Meiri D et al. Cannabis impacts tumor response rate to nivolumab in patients with advanced malignancies. Oncologist. 2019 Apr;24(4):549-554.
• No evidenceoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. of decreased survival, and weak evidenceone or more case studies, supported by animal evidence OR small treatment effects of limited clinical significance OR studies with no controls OR weak trends of effects (this is the CancerChoices definition; other researchers and studies may define this differently) of longer survival (not statistically significant), after first-line monotherapy pembrolizumab for metastatic disease among people with non-small cell lung cancer treated with cannabis compared to no cannabis in a mid-sized observational study³⁰Waissengrin B, Leshem Y et al. The use of medical cannabis concomitantly with immune checkpoint inhibitors in non-small cell lung cancer: a sigh of relief? European Journal of Cancer. 2023 Feb;180:52-61. 

Interactions with other therapies

CBD interacts with antiepileptic drugs, enhancing the bloodstream levels of some and reducing the level of others.³¹Gaston TE, Bebin EM et al. Interactions between cannabidiol and commonly used antiepileptic drugs. Epilepsia. 2017 Sep;58(9):1586-1592.

CancerChoices advisor Donald Abrams, MD, urges caution when using cannabis, especially concentrated, full-extract cannabis oil, due to its effect on detoxification enzymes and the ability of your liver to detoxify any other medications. See his commentary on potential interactions between CBD/THC and pharmaceuticals in Abrams DI. Cannabis, Cannabis, cannabinoids and cannabis-based medicines in cancer care. Integrative Cancer Therapies. 2022 Jan-Dec;21:15347354221081772.

Dependence and addiction

About 10% of people who use cannabis develop cannabis use disorder (addiction). People who use cannabis every day, or take high concentrations, are at the highest risk.³²Connor JP, Stjepanović D et al. Cannabis use and cannabis use disorder. Nature Reviews Disease Primers. 2021 Feb 25;7(1):16. Because THC is stored in fat and leaches out of the body fat to maintain a slowly diminishing blood level, people who use small amounts of cannabis typically do not get an abrupt withdrawal reaction if they stop.³³Abrams D. Email correspondence: Cannabis Abrams review. March 24, 2018. Withdrawal symptoms are typically mild and might include anxiety, insomnia, loss of appetite, migraine, irritability and restlessness.³⁴Crippa JA, Hallak JE et al. Cannabidiol for the treatment of cannabis withdrawal syndrome: a case report. Journal of Clinical Pharmacy and Therapeutics. 2013 Apr;38(2):162-4. CBD does not appear to cause addiction.³⁵Expert Committee on Drug Dependence. News Briefing – 40th WHO Expert Committee on Drug Dependence (ECDD). World Health Organization. September 13, 2018. Viewed October 9, 2021.

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