Melatonin for Cancer

Melatonin for Cancer: Safety & Side Effects

This page covers safety information for Melatonin. See our complete Melatonin therapy guide →

Authors

Nancy Hepp, MS

past Lead Researcher

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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 and writer for CancerChoices and also served as the first program manager. 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 past Lead Researcher

Sophie Kakarala

Research Assistant

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Sophie received her Bachelor of Arts from the University of Cambridge, where she studied Middle Eastern languages and the philosophy of science. She then completed a premedical post-baccalaureate at the City University of New York. Before joining CancerChoices, she worked for several years at the Cornell Center for Research on End-of-Life Care, where she helped to conduct research on terminal illness and grief. Working in end-of-life research filled her with the conviction that all patients deserve free, accessible, and scientifically accurate information about the therapies available to them. While taking classes in anthropology, she also became curious about traditional medical knowledge and philosophies. These interests led her to CancerChoices. She is delighted to be part of CancerChoices’s work creating rigorous, evidence-based treatment guides for patients and physicians.

Sophie Kakarala Research Assistant

Clinical reviewer

Dugald Seely, ND, MSc

Physician, researcher, and CancerChoices advisor

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Dugald Seely, ND, MSc is a naturopathic doctor and clinician scientist living in Ottawa, Canada. Dr. Seely serves patients living with cancer in clinic and is active in research building on the base of evidence for integrative and naturopathic oncology. Helping to pioneer the delivery and development of integrative oncology, Dr. Seely is the founder and executive director of The Centre for Health Innovation (CHI); an adjunct professor at the University of Ottawa, Faculty of Medicine; executive director for research and clinical epidemiology at the Canadian College of Naturopathic Medicine; and president of the Oncology Association of Naturopathic Physicians (OncANP). Dr. Seely has led numerous clinical trials and synthesis research over the past 18 years and has published and presented internationally. Dugald is the father of two and most happy when spending time with his family in the wild outdoors.

Dugald Seely, ND, MSc Physician, researcher, and CancerChoices advisor

Last update: July 22, 2026

Side effects and adverse reactions

Melatonin can cause daytime drowsiness and may increase the risk of falling among people with dementia.¹Givler D, Givler A et al. Chronic Administration of Melatonin: Physiological and Clinical Considerations. Neurology International. 2023 Mar 15;15(1):518-533. It can also cause intensified dreams, or more vivid dream memories. 

Melatonin appears to have both immune-activating and anti-inflammatory effects. This means its influence on autoimmune disorders like Crohn’s disease, myasthenia gravis, and rheumatoid arthritis is hard to predict. For this reason, it’s important to discuss taking melatonin with your physician if you have an autoimmune condition.²Ghareghani M, Dokoohaki S et al. Melatonin exacerbates acute experimental autoimmune encephalomyelitis by enhancing the serum levels of lactate: A potential biomarker of multiple sclerosis progression. Clinical and Experimental Pharmacology & Physiology. 2017 Jan;44(1):52-61; MacDonald IJ, Huang CC et al. Reconsidering the Role of Melatonin in Rheumatoid Arthritis. International Journal of Molecular Sciences. 2020 Apr 20;21(8):2877. 

A large observational study found a correlation between melatonin and heart failure, suggesting caution for use with heart disease.³Nnadi E, Masara M  et al. Effect of long-term melatonin supplementation on incidence of heart failure in patients with insomnia. Circulation. 2025;152(suppl_3):A4371606.

Drug interactions 

Melatonin may affect the way anesthesia works. If you are preparing for surgery, it is important to discuss melatonin use before surgery with your team.

In rare cases, melatonin can interact with heart medications, including nifedipine, a calcium channel blocker, to cause high blood pressure.⁴Minari TP, Pisani LP. Melatonin supplementation: new insights into health and disease. Sleep Breath. 2025 Apr 25;29(2):169. There is preliminary evidence that it reduces clotting factors in the blood, and therefore could interact with blood-thinning medications (anticoagulants) to cause bleeding.⁵Wirtz PH, Spillmann M, Bärtschi C, Ehlert U, von Känel R. Oral melatonin reduces blood coagulation activity: a placebo-controlled study in healthy young men. Journal of Pineal Research. 2008 Mar;44(2):127-33. 

Interactions with medications and other interventions are complex. Always consult with a healthcare professional before adding any new therapy to your regimen. To learn more about interactions visit one of the trusted resources below: 

• About Herbs ›
• EfficaSafe ›

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