For most people taking melatonin occasionally to help with sleep, short-term use does not appear to harm the heart. But a large 2025 study presented at an American Heart Association meeting raised a serious flag: adults with insomnia who used melatonin for a year or longer had roughly 90% higher odds of developing heart failure over five years compared to matched non-users. That finding has shifted the conversation from “melatonin is harmless” to “long-term use deserves caution.”
The picture is more nuanced than a simple yes or no. Melatonin has measurable effects on blood vessels, blood pressure, and heart rhythm, and some of those effects appear protective while others raise concern.
What the Long-Term Safety Data Shows
The study that drew the most attention reviewed five years of health records for more than 130,000 adults with insomnia who had taken melatonin for at least 12 months. Compared to non-users, the melatonin group had a 4.6% rate of new heart failure diagnoses versus 2.7% in the comparison group. Among those who did develop heart failure, melatonin users were nearly 3.5 times as likely to be hospitalized for it (19.0% vs. 6.6%). All-cause mortality was also higher: 7.8% in the melatonin group versus 4.3% among non-users over the five-year period.
These numbers are striking, but they come with an important caveat. This was an observational study, not a controlled experiment. People who take melatonin every night for years may have more severe insomnia, worse overall sleep, or other health issues that independently raise heart failure risk. The study can’t prove melatonin caused the outcomes. Still, it’s the largest dataset to date on long-term melatonin use and cardiovascular health, and it’s enough to warrant attention.
Marie-Pierre St-Onge, who chairs the writing group for the American Heart Association’s 2025 scientific statement on sleep health, noted that melatonin is not indicated for treating insomnia in the U.S. and “should not be taken chronically without a proper indication.”
How Melatonin Affects Blood Vessels
Melatonin interacts with specific receptors in blood vessel walls. Research on coronary arteries has identified melatonin type 2 (MT2) receptors located in the smooth muscle cells that control how wide or narrow your arteries are. When melatonin activates these receptors, it reduces the ability of nitric oxide, your body’s natural vessel-relaxing signal, to widen coronary arteries. In practical terms, melatonin can make coronary arteries slightly less responsive to the signals that keep them open and blood flowing freely.
This doesn’t mean melatonin constricts your arteries in a dangerous way at normal supplement doses. But it does mean the hormone has a real, measurable effect on vascular tone, particularly in the arteries that supply the heart muscle itself.
Melatonin and Blood Pressure
On the blood pressure front, the evidence leans positive. A randomized, double-blind trial published in the American Heart Association’s journal Hypertension tested 2.5 mg of melatonin taken one hour before bedtime in men with untreated high blood pressure. After three weeks of nightly use, systolic blood pressure during sleep dropped by 6 mm Hg and diastolic pressure dropped by 4 mm Hg compared to placebo. Heart rate was unaffected.
A few details matter here. A single dose of melatonin did nothing to blood pressure; the effect only showed up after consistent nightly use over three weeks. The blood pressure reduction was specific to sleep, with no significant change during waking hours. And the drop, while real, was modest. For context, a 5 mm Hg reduction in systolic blood pressure is generally associated with meaningful reductions in cardiovascular event risk at a population level, so even this modest effect could matter over time.
Effects on Heart Rhythm
One common worry is whether melatonin could trigger palpitations or abnormal heart rhythms. The available research suggests the opposite. In studies on atrial fibrillation (the most common type of irregular heartbeat), melatonin reduced the likelihood that the arrhythmia would develop, particularly in the context of sleep deprivation.
Sleep deprivation itself is a well-known trigger for atrial fibrillation. Melatonin appears to counteract this by reducing oxidative stress in the energy-producing structures of heart cells and normalizing calcium signaling, which is the electrical process that coordinates each heartbeat. In sleep-deprived models, melatonin corrected the electrical abnormalities that make the heart’s upper chambers vulnerable to fibrillation, including irregular conduction patterns and a phenomenon called “discordant alternans” where different regions of the heart beat out of sync.
These findings are largely from laboratory and animal research, and clinical trials in humans are still needed to confirm whether melatonin has practical anti-arrhythmic benefits. But they do suggest that occasional melatonin use is unlikely to cause heart rhythm problems.
Interactions With Heart Medications
If you take blood thinners, melatonin deserves extra caution. Limited data suggest melatonin may amplify the effects of warfarin. The World Health Organization’s monitoring center has documented six suspected interaction cases, four involving reduced blood clotting ability and two involving bleeding complications such as eye hemorrhage and nosebleeds. If you’re on warfarin and start or stop melatonin, your clotting levels may need to be checked more frequently.
The interaction profile with other heart medications is less well documented, but because melatonin has blood pressure-lowering effects during sleep, combining it with antihypertensive drugs could theoretically cause blood pressure to dip too low overnight. This is more of a concern for people already prone to low nighttime blood pressure or dizziness upon waking.
What This Means in Practice
The short version: occasional melatonin use for jet lag or a rough stretch of sleep is not something most people need to worry about from a heart standpoint. The blood pressure and heart rhythm data are, if anything, mildly encouraging for short-term use.
The concern is with chronic, long-term use. Taking melatonin every night for months or years puts you in the category where the observational data shows higher rates of heart failure and hospitalization. Whether melatonin is directly causing those outcomes or simply correlated with them remains unclear, but the signal is strong enough that using melatonin as a permanent nightly habit is worth reconsidering, especially if you have existing heart disease or risk factors for heart failure. If you’ve been taking melatonin nightly for a long time, it’s a reasonable topic to bring up with your doctor rather than something to abruptly stop on your own.