Melatonin for Sleep: Dosage, Timing, and the Heart Failure Question
Melatonin has been marketed for decades as the safest sleep aid on the shelf. That framing got complicated in November 2025, when researchers presented data at the American Heart Association's Scientific Sessions linking long-term melatonin use to a significantly higher rate of heart failure. The headlines were alarming; the actual study is more nuanced. Here's what the research found, why cardiologists are urging caution before drawing conclusions, and what dosage science still holds regardless.
Melatonin remains one of the most widely used sleep supplements in the U.S. — which is exactly why new safety data draws so much attention.
What the Heart Failure Study Actually Found
Researchers led by Dr. Ekenedilichukwu Nnadi, chief resident in internal medicine at SUNY Downstate/Kings County Primary Care, analyzed health records for more than 130,000 adults diagnosed with chronic insomnia using the TriNetX Global Research Network. Of that group, roughly 65,000 had been prescribed melatonin at least once and reported using it for a year or longer. Over five years of follow-up, that group showed an approximately 90% higher rate of heart failure diagnosis, more heart failure hospitalizations, and higher all-cause mortality compared to people with insomnia who hadn't used melatonin long-term.
"Melatonin supplements may not be as harmless as commonly assumed," Nnadi said when presenting the findings. "If our study is confirmed, this could affect how doctors counsel patients about sleep aids." The research was presented as a preliminary abstract, not yet peer-reviewed or published in a journal, which matters for how much weight to put on it right now.
Why Cardiologists Say Don't Panic Yet
The study measured association, not cause — and persistent insomnia itself can be an early sign of heart trouble, not just a result of it.
The study has real, acknowledged limitations. It's observational, meaning it can show a statistical association but cannot prove melatonin caused the heart failure. It didn't track the actual dosage patients took, or how severe their insomnia was. And the "non-user" comparison group could still include people taking over-the-counter melatonin without a prescription, since the data only captured prescribed use, muddying the comparison.
Cardiologists interviewed about the findings raised a specific alternative explanation: the direction of causation might run the other way. "Difficulty sleeping can be a symptom of existing heart failure," explained Dr. Kanika Mody, a heart failure and transplant specialist, noting that disease-related anxiety, medication side effects, and breathing difficulties can all disrupt sleep independent of melatonin. Needing melatonin nightly for over a year may be a marker that something else is going on, rather than melatonin itself doing the damage. A University of Rochester Medicine cardiologist made the same point, noting the people who took melatonin long-term may simply have had worse underlying sleep or health issues to begin with.
How Much Melatonin Actually Works
Separate from the heart failure question, dosage research has been fairly consistent for years: less is usually more. Store shelves are stocked with 3 to 10 mg tablets, but sleep researchers have repeatedly found that doses in the 0.3 to 1 mg range are enough to raise blood melatonin to normal nighttime levels and produce a measurable hypnotic effect — without pushing levels above what the body naturally produces. Once melatonin receptors are saturated, taking more doesn't meaningfully improve sleep; it mainly adds side effects like next-day grogginess, headaches, or vivid dreams.
Starting Dose
0.5 to 1 mg, taken 30 to 60 minutes before bed, is the level most sleep researchers now recommend starting with.
Typical Range
Most adults who need more find 1 to 3 mg effective; doses above 5 mg rarely add benefit and raise side-effect risk.
Timing Matters
Research on timing suggests taking melatonin a few hours before bed, not right at lights-out, may improve sleep-onset latency more reliably.
Best Use Case
Melatonin works best for a disrupted body clock — jet lag or delayed sleep phase — rather than as a general-purpose sedative.
There's no FDA-established maximum dose for adults, which is part of why store products range so widely. But the absence of a hard ceiling isn't the same as a recommendation to take more; it mainly reflects how under-regulated the supplement category is compared to prescription sleep medication.
Weighing the New Data Against the Old Habits
- Low-dose, short-term melatonin use has decades of safety data behind it
- It remains genuinely useful for jet lag and shift-work circadian disruption
- Low risk of dependence compared to prescription sleep medications
- Long-term (1+ year) nightly use no longer has a clean safety record
- Most people take doses several times higher than research supports
- Chronic reliance may be masking an underlying sleep or health issue
The practical takeaway isn't to panic or immediately stop melatonin. It's to treat chronic, nightly use the way you'd treat any other long-term medication habit: worth a conversation with a doctor, especially if it's been going on for a year or more, rather than an indefinite default because it's sold without a prescription.
Should You Still Take Melatonin?
For short-term, low-dose use, yes. For chronic nightly use, talk to a doctor first.
The 2025 heart failure findings are a real signal worth taking seriously, not a confirmed cause-and-effect result. They're most useful as a reason to question chronic, unsupervised use rather than a reason to abandon melatonin outright for jet lag or an occasional bad night. Combined with the long-standing dosage research, the clearest actionable change for most people is simple: take less than the bottle suggests, and treat months of nightly use as a cue to get the underlying sleep problem actually diagnosed.
Frequently Asked Questions
Does melatonin cause heart failure?
A 2025 American Heart Association study found long-term melatonin users had a 90% higher rate of heart failure diagnosis over five years, but the study was observational and cannot prove melatonin causes the condition. It hasn't been peer-reviewed, didn't track dosage, and researchers say chronic insomnia itself, not the supplement, may explain much of the link.
What is the correct melatonin dosage for sleep?
Most sleep researchers recommend starting with the lowest effective dose, typically 0.5 to 1 mg taken 30 to 60 minutes before bed, rather than the 3 to 10 mg doses common on store shelves. Studies suggest melatonin's sleep-promoting effect plateaus once receptors are saturated, so higher doses mainly add side effects without improving sleep further.
Is it safe to take melatonin every night long-term?
Long-term nightly use hasn't been well studied for cardiovascular safety, which is exactly what prompted the 2025 AHA research. Needing melatonin nightly for over a year is also a signal worth discussing with a doctor, since persistent insomnia can itself be a symptom of an underlying health issue.
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