You probably know that feeling of lying awake at 2 a.m., hunting for anything that might help you drift off.
For many Americans, that something is a melatonin gummy from a jar on the nightstand. It feels harmless, almost like a vitamin.
But a new 5-year analysis presented at the American Heart Association's Scientific Sessions 2025 tells a less reassuring story.
Adults with chronic insomnia who used melatonin for a year or more were about 90 percent more likely to develop heart failure than non-users.
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The study looked at electronic health records from 130,828 adults with insomnia, with an average age of 55.7 years. Around six in ten were women.
Those prescribed melatonin for at least a year were matched to similar adults who had not used it.
What the records actually showed
Over five years, heart failure turned up in 4.6 percent of long-term melatonin users, compared with 2.7 percent of non-users.
That is nearly a doubling of risk, though still a small share overall.
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Melatonin users were hospitalized for heart failure about 3.5 times as often as non-users. Deaths from any cause were also nearly twice as common in the melatonin group.
The findings are preliminary. The abstract has not yet been peer-reviewed, and the design was observational.
That means it can show a strong link, but cannot prove melatonin itself caused the heart problems.
Insomnia on its own raises heart risk, and people who end up on melatonin long-term may be sicker to begin with.
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The researchers tried to level the playing field by matching users and non-users on 40 health and lifestyle factors.
"Melatonin supplements may not be as harmless as commonly assumed. If our study is confirmed, this could affect how doctors counsel patients about sleep aids," said lead author Dr. Ekenedilichukwu Nnadi.
He is chief resident in internal medicine at SUNY Downstate/Kings County Primary Care in Brooklyn.
What this means for how long you take it
Even before this study, US health authorities were cautious about long-term use.
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The National Center for Complementary and Integrative Health says there is not enough strong evidence to recommend melatonin for chronic insomnia.
The agency also notes that long-term safety data is lacking. In the US, melatonin is sold as a dietary supplement, not a regulated drug.
Doses on the shelf vary wildly. A 2023 research letter in JAMA tested 25 melatonin gummy products and found that 22 were mislabeled. Actual amounts ranged from 74 percent to 347 percent of what the label claimed.
The new finding points at nightly, long-term use. It does not implicate taking melatonin for a few days of jet lag or shifting a work schedule. Short, occasional use was not the pattern studied.
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The full manuscript has not yet appeared in a peer-reviewed journal.
The authors say adults who have been taking melatonin nightly for months or years should raise it with their doctor before changing anything.
This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.