Medical cannabis and cannabinoids in raw or dried flowers, oils, capsules, powders, edibles, and topicals may reduce pain, and some evidence shows benefit with nausea, vomiting, and sleep, but little evidence of improving treatment outcomes.

Safety and precautions

We advise medical supervision and monitoring when using cannabis for medical purposes. Cannabis can impair driving and other tasks requiring judgment and rapid response, so caution is warranted.

Cancer promotion

Head, neck, and oral cancer

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 higher risk of oral cancer among people using cannabis

No evidence of an effectoverall, 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. on risk of head and neck cancer among people using cannabis in a combined analysis of 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) of higher risk of HPV-16-positive head and neck squamous cell carcinomas, but not HPV-16-negative carcinomas, among people using cannabis

Lung cancer

Weak evidence of a link between cannabis smoking and lung cancer

Testicular cancer

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 higher risk of testicular germ cell tumor (TGCT) and especially nonseminoma TGCT among people reporting use of cannabis

Side effects or adverse events

Interactions with cancer treatments

Modest evidence of worse response to immunotherapy among among people with advanced cancer using cannabis

Cardiovascular health effects

Smoking cannabis carries many of the same cardiovascular health hazards as smoking tobacco. While the level of evidence is modest, enough data has accumulated to advise caution in using cannabis for people at highest risk of cardiovascular events, including those who present with a heart attack or new arrhythmia, or who have been hospitalized with heart failure.11DeFilippis 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.

THC in cannabis is associated with endothelial dysfunction (a type of non-obstructive coronary artery disease).12Page RL 2nd, Allen LA et al. Medical marijuana, recreational cannabis, and cardiovascular health: a scientific statement from the American Heart Association. Circulation. 2020;CIR0000000000000883.

Other side effects

THC in cannabis can have these effects:13Page RL 2nd, Allen LA et al. Medical marijuana, recreational cannabis, and cardiovascular health: a scientific statement from the American Heart Association. Circulation. 2020;CIR0000000000000883.

  • Sympathetic nervous system (“fight or flight”) stimulation, which increases heart rate, myocardial oxygen demand, blood pressure, and platelet activation
  • Parasympathetic nervous system (“rest and digest”) inhibition
  • Associated with endothelial dysfunction (a type of non-obstructive coronary artery disease) and oxidative stress
  • Higher risk of psychosis with use of high potency (high TCH) products compared to low-potency14Petrilli 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.

People treated with THC for pain withdrew from treatment due to adverse side effects more often than controls, with a higher likelihood of withdrawal among people treated with THC extracted from cannabis compared to synthetic THC 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 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 effects.15McDonagh MS, Morasco BJ et al. Cannabis-based products for chronic pain: a systematic review. Annals of Internal Medicine. 2022 Jun 7.

According to CAM-Cancer, “A number of adverse events have been observed after the intake of medical cannabis and cannabinoids. Some may be welcome, such as mood enhancement or sedation.”16Horneber M, Landwehr C, Kalbermatten Magaya N, Ritter C, Ziemann C. Medical cannabis and cannabinoids. CAM-Cancer. September 10, 2020. Viewed October 9, 2021. Side effects include these:

  • Dry mouth
  • Dizziness
  • Sleepiness or drowsiness (somnolence) 
  • Fatigue or lack of energy (lethargy)
  • Vomiting
  • Fever
  • Elevated liver values

Effects found in reviews of studies

Side effects as a whole

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 more adverse side effects among people treated with cannabis for pain or chemotherapy-induced nausea and vomiting

Cognitive impairment

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) of slightly higher risk of short-term cognitive impairment and impaired attention among people with chronic pain or cancer treated with oral cannabis

Drowsiness or sedation

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) of higher risks of sleepiness or drowsiness among people using cannabis

Gastrointestinal symptoms

Good evidence of higher risk of nausea and vomiting among people treated with oral cannabis

Neurological side effects

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) of nervous system side effects among people treated with medical cannabis

Good evidence of euphoria among people using cannabinoids

Modest evidence of higher rates of dizziness, dysphoria, or disorientation among people treated with cannabis for chemotherapy-induced nausea and vomiting

Preliminary evidence of nervous system side effects among people treated with medical cannabis

No evidenceoverall, one or more studies did not demonstrate that a treatment or intervention led to higher risk; 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 higher risk of psychiatric disease among people using cannabinoids in combined analyses of studies

Modest and somewhat conflicting evidence of higher risk of dizziness or disorientation among people treated with oral cannabis

Oral tissue damage

Preliminary evidence of harm to the tissues that both surround and support the teeth among people who smoke cannabis

Interactions with other therapies

CBD interacts with antiepileptic drugs, enhancing the serum levels of some and reducing the level of others.40Gaston TE, Bebin EM et al. Interactions between cannabidiol and commonly used antiepileptic drugs. Epilepsia. 2017 Sep;58(9):1586-1592.

Dependence and addiction

Using cannabis can lead to substance use disorders such as physical and/or psychological dependence in some people.41Wagener D. Marijuana Addiction Facts: Is Marijuana Physically Addictive? American Addiction Centers. August 26, 2021. Viewed October 9, 2021; National Institute on Drug Abuse. Marijuana Research Report: Is marijuana addictive? July 2020. Viewed October 9, 2021. Physical dependence on cannabis can develop with sustained use.42Grotenhermen F. Pharmacokinetics and pharmacodynamics of cannabinoids. Clinical Pharmacokinetics. 2003;42(4):327-60. High potency (high TCH) products are linked to a higher risk of cannabis use disorder compared to low-potency products.43Petrilli 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.

Regular cannabis users who wish to discontinue use should speak with a doctor for a medically supervised cessation plan.

CBD shows no indications for addiction or dependence in humans.44Expert Committee on Drug Dependence. News Briefing—40th WHO Expert Committee on Drug Dependence (ECDD). World Health Organization. September 13, 2018. Viewed October 9, 2021.

Resource

Wellkasa

Wellkasa provides information on interactions among hundreds of natural products, over-the-counter drugs, and prescription medications.

Cannabis

Keep reading about cannabis and cannabinoids

Authors

Nancy Hepp, MS

Lead Researcher and Program Manager
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Ms. Hepp is a researcher and communicator who has been writing and editing educational content on varied health topics for more than 20 years. She serves as lead researcher, program manager, and writer for CancerChoices. Her graduate work in research and cognitive psychology, her master’s degree in instructional design, and her certificate in web design have all guided her in writing and presenting information for a wide variety of audiences and uses. Nancy’s service as faculty development coordinator in the Department of Family Medicine at Wright State University also provided experience in medical research, plus insights into medical education and medical care from the professional’s perspective.

Nancy Hepp, MS Lead Researcher and Program Manager

Laura Pole, RN, MSN, OCNS

Senior Clinical Consultant
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Laura Pole is senior clinical consultant for CancerChoices. Laura is an oncology clinical nurse specialist who has been providing integrative oncology clinical care, navigation, consultation, and education services for over 40 years. She is the co-creator and co-coordinator of the Integrative Oncology Navigation Training at Smith Center for Healing and the Arts in Washington, DC. Laura also manages the “Media Watch Cancer News That You Can Use” listserv for Smith Center/Commonweal. In her role as a palliative care educator and consultant, Laura has served as statewide Respecting Choices Faculty for the Virginia POST (Physician Orders for Scope of Treatment) Collaborative as well as provided statewide professional education on palliative and end-of-life care for the Virginia Association for Hospices and Palliative Care.

For CancerChoices, Laura curates content and research, networks with clinical and organizational partners, brings awareness and education of integrative oncology at professional and patient conferences and programs, and translates research into information relevant to the patient experience as well as clinical practice.

Laura sees her work with CancerChoices as a perfect alignment of all her passions, knowledge and skills in integrative oncology care. She is honored to serve you.

Laura Pole, RN, MSN, OCNS Senior Clinical Consultant

Reviewer

Teresa Martin

Integrative patient advocate
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Teresa Martin, founder of Options Patient Advocacy, is an integrative patient advocate that helps patients find specialists and integrative healthcare professionals close to where they live. Scientifically educated, and passionate about patient-centered care, Teresa’s focus areas include integrative oncology, chronic lymphocytic leukemia, and condition-specific applications of medical cannabis.

Teresa Martin Integrative patient advocate

Last update: October 24, 2022

Last full literature review: October 2021

We are grateful to integrative oncologist and CancerChoices advisor Donald Abrams, MD, for his generous sharing of research articles and commentary.

CancerChoices provides information about integrative in cancer care, a patient-centered approach combining the best of conventional care, self care and evidence-informed complementary care in an integrated plan cancer care. We review complementaryin cancer care, complementary care involves the use of therapies intended to enhance or add to standard conventional treatments; examples include supplements, mind-body approaches such as yoga or psychosocial therapy, and acupuncture therapies and self-care lifestyle actions and behaviors that may impact cancer outcomes; examples include eating health-promoting foods, limiting alcohol, increasing physical activity, and managing stress practices to help patients and professionals explore and integrate the best combination of conventionalthe cancer care offered by conventionally trained physicians and most hospitals; examples are chemotherapy, surgery, and radiotherapy and complementary therapies and practices for each person.

Our staff have no financial conflicts of interest to declare. We receive no funds from any manufacturers or retailers gaining financial profit by promoting or discouraging therapies mentioned on this site.

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