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Question & Answer

Can cannabis cure cancer?
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The Evidence

  • Cannabis can be made from the dried flowers, leaves, stems and seeds of a plant called Cannabis sativa. The plant contains more than 500 chemical substances.
  • Doctors can prescribe cannabis to treat symptoms in people with certain conditions, such as multiple sclerosis and chronic pain.
  • We were asked if cannabis can cure cancer.
  • We found six systematic reviews on this topic.
  • One moderate-quality review looked at three studies of cannabis in combination with other medicines and two studies of cannabis alone:
    • Survival – One study reported that people who took cannabis lived longer than those who didn’t, one reported the opposite and one did not find a difference.
    • Tumour progression (growth and spread) – One study found that the tumours of people taking cannabis progressed more quickly than in those who did not take cannabis, and two studies found there was no difference. However, the studies in this review did not include many people, and the studies were not high-quality randomised controlled trials(RCTs), so we can’t be sure of these findings.
  • The second review looked at using cannabis in people with cancer of the brain and spinal cord and found that there was no difference in the risk of dying after one year between people who took cannabis and those who did not. However, most of the studies were not RCTs.
  • The third review looked mostly at case reports or case series, which are not good enough to figure out whether cannabis can work as an anti-cancer treatment or not.
  • The fourth review included studies that are already in the reviews above. The only new information was from a single case of a brain tumour which reduced after cannabis but the evidence is not good enough to say if cannabis can cure cancer as it may have happened by chance.
  • The fifth and sixth reviews didn’t have any further studies apart from those already included in the reviews above.

Guidelines and recommendations

  • We found some information from the World Health Organization, which said that cannabis can help with nausea and vomiting in people with advanced AIDS, cancer and other illnesses. However, they did not say anything about whether cannabis can be used to treat cancer.

Things to Remember

  • Watch out for studies based on a small number of people, they can’t really tell us if a treatment works or not.
  • If someone tells you they got better after using a treatment, it does not necessarily mean that the treatment made them better.
  • Look out for comparisons of treatments between studies that are different.

Reviewers

  • Lead Researcher: Dr. Paula Byrne, Senior post-doctoral researcher, iHealthFacts, Evidence Synthesis Ireland and Cochrane Ireland, College of Medicine, Nursing and Health Sciences, University of Galway.
  • Reviewed by: Dr. Kayleigh Kew, Freelance researcher in evidence synthesis methods and technology, UK
  • Topic advisor: Prof. Emma Wallace, Professor of General Practice, Dept of General Practice, University College Cork & General Practitioner, Parklands Surgery, Commons Road, Cork.
  • Public and Patient advisor: Deirdre Mac Loughlin, Public and Patient Involvement in research (PPI) advisor, PPI Ignite, University of Galway.
  • Journalist Advisor: Dr. Claire O’Connell, PhD in cell biology, Masters in Science Communication. Contributor to The Irish Times, writing about health, science and innovation.

Conflict of Interest Statement: The authors have no financial or other conflicts of interest for this health claim summary.

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