There are over 2,000 scientific publications on melatonin and cancer. Some of these are laboratory studies, but there are also many human studies. So what do the results show? Let’s look today at whether melatonin can help when combined with chemotherapy.

When there is a large volume of research published, it is often useful to look at the results of meta-analysis trials, as these combine the results of similar trials to see the consistency between the results. One such trial [1] looked at eight different randomized controlled trials of melatonin for solid tumors. 

Study design

The meta-analysis looked at published studies that used melatonin concurrently with chemotherapy or radiotherapy for cancer. They identified eight studies that satisfied their criteria. They then examined the pooled results to see what effect melatonin had on tumor remission, 1-year survival, and side effects. The total number of patients was 761.

Of the eight studies selected, seven of them used chemotherapy and only one (on brain glioblastoma) used radiotherapy. The types of cancers investigated were lung, breast, gastrointestinal, head, neck, liver, colorectal, and glioblastoma. All the cancers were either advanced or metastatic.

The dose level of melatonin used in all of the studies was 20mg/day, taken at night. 


Melatonin significantly improved:

  • the complete and partial remission rate – chemo/radiation only (C/R) 16.5% vs chemo/radiation with melatonin (C/R+Mel) 32.6%
  • 1 year survival rate – C/R 28.4% vs C/R + Mel 52.2%
  • and significantly decreased rate of radiation and chemo side effects including:
    • thrombocytopenia C/R 19.7% vs C/R+ Mel 2.2%
    • neurotoxicity C/R 15.2%  vs C/R + Mel 2.5%
    • fatigue C/R 49.1% vs C/R +Mel 17.2%

The table at the beginning of this blog post shows the results.

These effects were consistent across different types of cancer.

These results are significant. Melatonin is seen to not only reduce side effects of chemo and radiation but also to improve the outcome of treatment. AND this was all in advanced or metastatic cancer. 

Dose level of melatonin

For all studies, the dose level tested was 20mg at night. This is a much higher dose level than is used to improve circadian rhythm and sleep (often 0.5-3mg).  The 20mg dose level is often referred to as the “pharmaceutical” level – as at this higher dose level, it is showing anti-cancer effects. 

At this dose level, no significant adverse effects were seen, and it is considered safe. Its effects on sleep mean that it is better to administer at night time so any sedating effects are during the night when we want to sleep anyhow. 


This meta-analysis indicates a consistent effect of melatonin in improving tumor remission, improving 1-year survival, and reducing side effects in a variety of advanced stage cancers.

One of the limitations of this study is that six of the eight studies were performed in the same center. This is often seen where one group leads the research in a particular field.  In this case, Dr Paolo Lissoni is the key scientist for the majority of the studies.  He is chief of radiation oncology at a large hospital in Italy and is the world’s leading proponent on melatonin and cancer.  He has published more than 300 journal articles, with more than 100 on melatonin.  When there is a key leader in this field of research like this, it is not surprising that they have conducted the majority of studies.  As many of his findings have subsequently been replicated by others, this suggests that this bias towards one group doesn’t necessarily affect the credibility of the studies.

In conclusion, melatonin in conjunction with chemotherapy or radiation seems to be beneficial in patients with solid cancers, doubling the remission rate, 1-year survival and reducing toxicity. Because of its low cost, excellent patient tolerability, and mild toxicity, melatonin is a rational inclusion in integrative oncology treatment plans for solid tumors. However, as always, it would be good to see more randomized trials to verify these findings.  

Who should avoid supplemental melatonin?

Avoid taking melatonin if you: 

  • have bipolar disease  
  • are a child 
  • are pregnant or lactating, as melatonin has effects on estrogen (which is why it is helpful with breast cancer)

If you fit into one of these categories, melatonin use should be under the supervision of your doctor.  


It may help to work with an integrative oncologist, naturopath, oncology nutritionist or cancer guide if you want to try melatonin for its anti-cancer effects. I find it useful for many of my clients. 

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[1] Wang, Y., Jin, B-Z., Ai, F. et al. (2012). The efficacy and safety of melatonin in concurrent chemotherapy or radiotherapy for solid tumors: a meta-analysis of randomized controlled trials. Cancer Chemother Pharmacol, 69(5), 1213-1220. 

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