For most people taking melatonin occasionally to fall asleep, short-term use has not been shown to harm the heart. Some evidence even suggests melatonin can modestly lower blood pressure and improve blood vessel function. But a large 2025 study presented at an American Heart Association conference found that long-term daily use (a year or more) was linked to a significantly higher risk of heart failure, raising real questions about whether chronic melatonin use is as safe as people assume.
The picture is more nuanced than a simple yes or no. Here’s what the research actually shows about melatonin and your cardiovascular system.
How Melatonin Affects Your Blood Vessels
Melatonin interacts with two types of receptors in your blood vessel walls, called MT1 and MT2, and they do opposite things. When melatonin activates MT1 receptors, blood vessels constrict (narrow). When it activates MT2 receptors, blood vessels dilate (widen). The net effect on your circulation depends on the relative number of each receptor type in a given part of the body, and researchers still don’t have a complete map of how those receptors are distributed in human tissues.
This dual action helps explain why melatonin’s cardiovascular effects aren’t straightforward. In the forearm, for example, MT2 receptors appear to outnumber MT1 receptors, so the overall effect is vessel relaxation. Other vascular beds may respond differently.
The Blood Pressure Effect
A meta-analysis of randomized controlled trials found that controlled-release melatonin (the kind that dissolves slowly overnight) reduced nighttime systolic blood pressure by about 6 mmHg and diastolic pressure by about 3.5 mmHg. Those are meaningful reductions, roughly comparable to what you’d get from cutting sodium intake or losing a few pounds. Fast-release melatonin, by contrast, had essentially no effect on blood pressure.
This distinction matters. Your body naturally releases melatonin in a slow, sustained pattern overnight. A controlled-release supplement mimics that pattern, while a fast-release pill creates a brief spike that fades quickly. If blood pressure benefits are what you’re after, the formulation makes a difference.
Cholesterol and Triglycerides
A systematic review of eight randomized controlled trials found that melatonin supplementation lowered triglycerides by about 32 mg/dL and total cholesterol by about 18 mg/dL. Those effects were most pronounced at doses of 8 mg per day or higher, in trials lasting at least 8 weeks, and in people who started with elevated cholesterol (200 mg/dL or above). There was no significant change in LDL (“bad” cholesterol) or HDL (“good” cholesterol) individually.
Blood Vessel Flexibility
Healthy blood vessels expand and contract easily in response to blood flow. In people with heart failure, this flexibility deteriorates because oxidative stress breaks down the signaling molecules that keep vessel walls supple. A randomized, double-blinded trial tested 10 mg of melatonin daily for 24 weeks in heart failure patients and found a meaningful improvement in vessel flexibility compared to placebo. The melatonin group gained about 1.6 percentage points in flow-mediated dilation (a standard measure of vessel health), while the placebo group actually declined by 1.4 points. The benefit was minimal in patients who also had diabetes.
The Heart Failure Concern
The most worrying data comes from a large observational study of more than 130,000 people with insomnia, presented at an American Heart Association conference in 2025. Researchers compared people who used melatonin for at least 365 days against matched controls who never used it, then tracked outcomes over five years. The results were striking: melatonin users had an 89% higher rate of developing heart failure (4.6% vs. 2.7%), a threefold increase in heart failure hospitalizations (19% vs. 6.6%), and roughly double the rate of death from any cause (7.8% vs. 4.3%).
The researchers matched the two groups on more than 40 baseline health variables to reduce confounding, and the results held up in sensitivity analyses. Still, this is an observational study, not a randomized trial. It’s possible that people who take melatonin every night for years have underlying health issues (beyond insomnia) that independently raise heart failure risk. But the size of the effect and the rigor of the matching make this hard to dismiss.
The American Heart Association highlighted this study with a pointed message: melatonin supplements “may not be as harmless as commonly assumed,” and long-term cardiovascular safety data are lacking. One of the researchers noted that melatonin is not even indicated for treating insomnia in the U.S., yet many people use it nightly for years.
Melatonin and Heart Rhythm
There is limited but notable evidence that melatonin can trigger abnormal heart rhythms in some people. A case report published in the Journal of Cardiovascular Pharmacology described two patients with structurally normal hearts who developed frequent premature ventricular contractions (PVCs), a type of extra heartbeat that feels like a flutter or skipped beat, while taking just 1 mg of melatonin daily. One patient had over 2,000 PVCs per day. In both cases, stopping melatonin completely eliminated the extra heartbeats, confirmed by continuous heart monitoring.
Two cases don’t prove melatonin commonly causes rhythm problems, but they represent the first documented human evidence that it can act as a trigger. If you’ve noticed palpitations after starting melatonin, this is worth paying attention to.
Interactions With Heart Medications
If you take blood thinners like warfarin, combining them with melatonin may affect how well your blood clots. A pilot study of 10 patients taking both drugs found that melatonin altered clotting time measurements enough to be clinically relevant, even though no one in the study actually experienced bleeding. Six of the ten patients had possible drug interactions, and two had probable interactions. Anyone on warfarin or similar medications should have their clotting levels monitored more closely if they add melatonin.
What This Means in Practice
The short-term cardiovascular profile of melatonin looks largely favorable: modest blood pressure reduction, improved vessel flexibility, lower triglycerides. These are all things that, in theory, protect the heart. The problem is that short-term benefits in small clinical trials don’t necessarily predict what happens when millions of people take a supplement every night for years.
The long-term observational data paint a more cautious picture. An 89% increase in heart failure risk over five years is a large signal, even if it needs confirmation from randomized trials. The practical takeaway is that occasional or short-term melatonin use for jet lag or a rough stretch of sleep is a very different proposition from taking it nightly as a permanent sleep solution. If you’ve been using melatonin daily for months or years, the emerging evidence suggests it’s worth reconsidering that habit, especially if you have existing heart disease or risk factors.