Many people take melatonin to treat your problems insomnia. It is usually offered as a natural supplementwithout risks. In fact, in countries like Spain you can buy without a medical prescription. However, according to a study to be presented this week at the American Heart Association Scientific Sessions 2025his long term consumption It could cause a side effect that we didn’t realize.

In the study in question they participated 130,000 people from the United States and the United Kingdomcountries in which it can be purchased freely or with a prescription, respectively. The health data of those patients who had taken melatonin for at least a year were compared with that of those who, despite also having insomnia, had not resorted to this supplement. Thus, it was seen that the risk of heart failure or death was significantly higher in the first group.

It should be noted that It is an observational study in which a relationship has been found, but not a cause. Therefore, it cannot be ruled out that it is a simple coincidence.

Why do so many people take melatonin?

Melatonin is a hormone that we produce naturally in our pineal gland. He is one of the main actors in the sleep regulation through circadian rhythms. That is, in 24-hour cycles. When light enters through our eyes, the brain interprets that it is daytime and inhibits the release of melatoninsince it is the hormone that helps us fall asleep. On the other hand, as the light passing through the eyes is reduced, melatonin begins to be released and little by little we feel drowsy.

Sometimes people who work night shifts, so they have to sleep during the day, may require melatonin in supplements, since they do not release enough naturally. On other occasions, we may need it because the rooms in our house are too lit at night, but that is a problem that is solved by lowering the intensity of the lights and, above all, changing cold lights for warmer ones. Bluish light is what inhibits melatonin to the greatest extent.

And other times insomnia can be due to many reasons that are not directly related to melatonin. Therefore, although it is sometimes used, it may be unnecessary. It is usually thought that nothing happens, that after all it is a hormone that we produce and, therefore, a natural supplement. But it may not be as harmless as we think.

Not everything natural is harmless

Hemlock is as natural as lettuce, but not exactly harmless. That said, it is true that until now they are not known Serious side effects associated with the consumption of melatonin supplements. However, in the study that will be presented this week they saw several data that could be alarming.

As we have already mentioned, they analyzed the data from 130,000 people registered in health data banks. All of them had insomnia, but not all of them took melatonin supplements. None of them had previous cardiovascular problems, since those who did were excluded from the study.

When comparing those who took melatonin with those who did not, it was observed that in those patients whose electronic health records indicated long-term melatonin use (12 months or more) there were approximately 90% more likely to suffer heart failure over the next 5 years compared to non-melatonin users.

Be careful, there are limitations

This study has several limitations recognized by its authors. The first is that No causes beyond correlation have been found. On the other hand, only the electronic prescription records. This is a good measure in the United Kingdom, where melatonin can only be purchased with a prescription, so all cases would be included. However, in the United States can be purchased freelyso it may be that some of the patients with insomnia who registered as non-users were taking it.

Finally, it is important to take into account an important fact so that there is no panic. And 90% may seem outrageous, but we should not visualize it as if 9 out of 10 patients who took melatonin had heart problems. The risk was 90% higher compared to those who did not take it, but the risk was low in both groups. 90% of something very low is still low.

Even so, this study justifies that more attention should be paid to the side effects of melatonin. At the very least, the population should be educated to resort to it only as a last measure. Because, as we have already seen, sometimes it is enough to change a few light bulbs. Let’s use it only when we see no other way out and, if in doubt, always consult our doctor.