There is no clinical evidence that melatonin supplements cause dry eyes. In fact, the available research points in the opposite direction: melatonin appears to protect the surface of the eye from the kind of damage that leads to dryness. If you’re experiencing dry eyes after starting melatonin, the underlying reason you’re taking it, particularly poor sleep, is a more likely culprit.
What the Research Actually Shows
Rather than harming the eyes, melatonin has shown protective effects on the ocular surface in multiple lab and animal studies. In one study published in the Journal of Cellular and Molecular Medicine, melatonin reduced harmful reactive oxygen species on eye surface cells by roughly 20% under drying conditions, while doubling the activity of key antioxidant enzymes. It also significantly lowered levels of several inflammatory markers associated with dry eye disease, including TNF-α, IL-8, and IFN-γ.
Melatonin is naturally present in human tears, with concentrations that fluctuate throughout the day, rising from about 0.8 μmol/L in the morning to 1.67 μmol/L at night. This natural presence suggests the eye uses melatonin as part of its own defense system. When researchers applied melatonin topically to rabbit eyes along with a natural tear component, it stimulated tear secretion. A separate 2019 study found that melatonin and its analogs could promote tear production by volume.
A 30-day study in dogs given daily oral melatonin found no effect on tear production, no changes in eye pressure, and no adverse eye effects at all. The researchers specifically monitored for ocular side effects and found none.
How Melatonin Protects the Eye Surface
Dry eye disease involves two core problems: oxidative stress (cell damage from unstable molecules) and chronic inflammation on the surface of the eye. Melatonin works against both. It activates a cellular defense pathway that boosts the production of protective enzymes, essentially strengthening the eye’s ability to resist damage from drying out. It also tamps down the inflammatory signals that make dry eye progressively worse.
The oil-producing glands along your eyelid margins are another important piece of the dry eye puzzle. These glands secrete a thin lipid layer that keeps tears from evaporating too quickly. When inflamed, they overproduce abnormal lipids that destabilize the tear film. Research on human cells from these glands found that melatonin reduced inflammation-driven lipid overproduction and prevented the buildup of abnormal lipid droplets, without disrupting normal lipid output. This suggests melatonin could actually help maintain a healthier tear film rather than degrade it.
Why Your Eyes Might Feel Dry Anyway
If you started taking melatonin and noticed dry eyes around the same time, the more likely explanation is the sleep problem that led you to melatonin in the first place. Sleep deprivation has a well-documented relationship with dry eye disease. Lack of sleep makes tears more concentrated (hypertonic), shortens the time your tear film stays stable between blinks, and directly reduces tear secretion. As sleep deprivation continues, the lacrimal glands that produce tears become swollen and dysfunctional, with measurable changes in their lipid metabolism and protein output.
There’s also a screen time factor. People with sleep problems tend to spend more time on electronic devices in bed, and prolonged screen use shortens tear film breakup time, causing or worsening dry eye. The prevalence of sleep disorders is significantly higher among people with dry eye, and the two conditions share overlapping inflammatory pathways. Depression and anxiety, which commonly accompany sleep problems, are also correlated with dry eye severity.
One interesting detail: after a full night of sleep, both normal and dry-eyed patients show elevated tear levels and improved tear film stability upon waking. Sleep itself acts as a reset for the tear system. So if your sleep quality remains poor despite taking melatonin, your eyes are missing out on that nightly recovery period.
Other Possible Causes to Consider
Several common factors can trigger dry eyes that happen to coincide with starting a new supplement:
- Seasonal changes: Dry indoor heating in winter or increased air conditioning use can dehydrate the eye surface.
- Antihistamines and decongestants: These reduce mucus and fluid production throughout the body, including in the eyes.
- Increased screen time: Blink rate drops by as much as half during focused screen work, accelerating tear evaporation.
- Aging: Tear production naturally declines over time, particularly after age 50 and more markedly in women after menopause.
- Contact lens wear: Lenses can disrupt the tear film and reduce oxygen reaching the cornea.
What to Do if You Notice Dry Eyes
Since melatonin is unlikely to be the cause, stopping it may not resolve the dryness, and doing so could worsen sleep problems that are actually contributing to your symptoms. A more productive approach is addressing the dry eyes directly while continuing to work on sleep quality.
Preservative-free artificial tears used a few times daily can supplement your natural tear film. Keeping your sleeping environment humidified, especially in dry climates or heated rooms, helps prevent overnight evaporation. If you spend long hours at a screen, the 20-20-20 rule (every 20 minutes, look at something 20 feet away for 20 seconds) gives your blink rate a chance to recover. Omega-3 fatty acids from fish or flaxseed have shown modest benefits for tear quality in some studies.
If dryness persists or worsens, an eye care provider can measure your tear production and evaluate your oil glands to identify the specific type of dry eye you’re dealing with. That distinction matters because evaporative dry eye (from poor oil production) and aqueous-deficient dry eye (from low tear volume) respond to different treatments.