Melatonin Study Raises Safety Questions: What the Evidence Really Shows

Due to a recent melatonin study there has been a lot of talk about a well-known supplement, melatonin.  The study concluded that “long-term melatonin supplementation for insomnia was associated with an 89% higher hazard of incident heart failure, a three-fold increase in HF-related hospitalizations, and a doubling of all-cause mortality over 5 years”.   Pretty serious, and scary sounding statements.  However, it’s important to note this preliminary study had serious flaws, and it has not been peer-reviewed.  It proves causation, not correlation (e.g. fire trucks are more likely to be at a house on fire, rather than a house not on fire  – there’s a correlation, but it does that mean the fire trucks caused the fire).  It’s also important to note that there’s contradictory existing research to suggest that melatonin might have benefits for those with heart failure.

It is important to note that this preliminary study has not been peer-reviewed. It also was not a randomly controlled study (randomly assigning participants to groups to minimize bias and establish causality), it was an observational study (more practical to run but less likely to establish causality).

A recent study raised concerns about long-term melatonin use, but the design of the study makes its findings hard to interpret. It was observational, not randomized, and several important factors—such as insomnia severity, dosing, and self-supplementation—were not accounted for. Melatonin can be useful in certain situations, but it is a hormone and should be used thoughtfully and at the lowest effective dose. If you rely on melatonin regularly, it’s a good idea to review your individual case with a qualified practitioner.


— Mychael Seubert, ND

Some additional problems with the study include:

In some countries melatonin is a prescription, in others like the US, melatonin is available over the counter.  The study did not confirm that those classified as “not taking melatonin” were actually not taking melatonin – many may have been taking it on their own.

We already know insomnia increases the risk of heart failure and all-cause mortality so those individuals are already in a higher risk category.  Additionally, the study did not include the severity of their insomnia.   It is quite likely that those prescribed melatonin had more severe insomnia symptoms than those with insomnia who were not prescribed melatonin.  It is also likely that those with insomnia were more likely to take melatonin on their own where a prescription is not required. This would further blur the findings of the study.

They also did not note whether patients using melatonin experienced an improvement in sleep.  Perhaps those individuals with improved sleep vs those without improvement had a lower risk of these concerns?  It also did not note how much melatonin was used by individuals.

The study has serious flaws and should not have gotten the press it has gotten so far – I do not think it is time to panic at this point.  I do think it’s worth looking into more to make sure these findings are due to the poor nature of the study and not in fact real risks.  At this point there is substantial research demonstrating both the usefulness and safety of melatonin.  However, it is a hormone and should be used judiciously.  This would include trying non-hormonal options (depending on the case), only using melatonin long-term if it is benefitting someone and at the lowest dose that is effective.  I would not, in general, take it long term if it is not clearly benefitting. As always it’s best to discuss your individual case with your doctor or explore holistic sleep-support strategies.