The Signal of Darkness: How Melatonin Went From Frog Skin to Flight Plans—and What That Means for Your Nights

From a tadpole's skin to a human clock

In 1958, dermatologist Aaron Lerner isolated a mysterious pineal compound that blanched frog skin. He named it "melatonin," thinking it might treat skin disease. It didn't—but his discovery cracked open an entirely new language of night in biology. Within a year, Lerner and colleagues mapped its structure, and over the next decade the pineal gland's nightly melatonin release was recognized as a timecode for the body. In other words, melatonin wasn't a knockout drug; it was the darkness signal itself. ^[1][3][2]

What melatonin actually does (and doesn't)

Melatonin rises in the evening under control of the brain's master clock and darkness-sensitive eye cells. It tells tissues to switch into "night mode," helping coordinate sleep timing, metabolism, and hormone rhythms. That's why sleep physicians emphasize melatonin for shifting circadian timing—not as a general-purpose sleeping pill. As the American Academy of Sleep Medicine explains, it can help with jet lag, delayed sleep–wake phase, some shift-work problems, and certain pediatric sleep disorders—when timing is precise. ^[7]

Two experts put it plainly. Harvard's Steven Lockley: "It's not a very good sleeping pill... it's really only very useful at resetting the clock." ^[8] And Michael Grandner, University of Arizona: "Melatonin is almost never an appropriate supplement to treat insomnia... in clinical studies, it's generally not better than a placebo." ^[11]

Where it shines: moving the clock

For jet lag, evidence is unusually strong. A Cochrane review of randomized trials found melatonin—taken at local bedtime at your destination—reduced jet lag across eastbound long-haul flights; doses from 0.5–5 mg worked, with higher doses helping some people fall asleep faster. The number needed to treat was about two in trials that reported it. Timing is critical: take it at the wrong time and you can push your clock the wrong way. ^[4]

For delayed sleep–wake phase disorder (the archetypal "night owl" pattern), a double-blind trial pairing behavioral scheduling with melatonin advanced sleep onset by about 34 minutes and improved function versus placebo. The pill wasn't knocking participants out; it was nudging their internal night earlier so sleep arrived more readily. ^[6]

In children with autism spectrum disorder, prolonged-release melatonin improved sleep duration and caregiver quality-of-life in controlled trials, with dose-guided night-time use under clinical supervision. ^[9][10]

And a real-world story from the clinic underscores melatonin's role as a clock tool: a sighted graduate student with non-24-hour sleep-wake disorder—his sleep time drifting later each day—stabilized after timed nightly melatonin. ^[22]

The twist: a night signal collides with dinner

Here's a surprise many health-conscious readers miss: take melatonin near meals and you can nudge blood sugar the wrong way. In a randomized crossover study, a 5-mg dose impaired glucose tolerance both morning and evening during standard glucose testing. The mechanism looked different by time—less insulin release in the morning, more insulin resistance at night—but the takeaway is clear: avoid pairing melatonin with carbs. ^[5]

The plot thickens with genetics and mealtime. In a large crossover study designed to mimic early versus late dinner, eating close to bedtime (when endogenous melatonin is high) worsened glucose tolerance—especially in people with a common melatonin-receptor variant linked to type 2 diabetes risk—primarily by blunting insulin secretion. Earlier dinner fared better. ^[12][13]

Quality control in the wild

Because melatonin is sold as a dietary supplement in the U.S., what's on the label may not match what's in the bottle. A 2023 JAMA analysis of U.S. melatonin gummies found 88% inaccurately labeled—some with 3.5× the stated dose and one with no melatonin at all. ^[15] A prior laboratory survey showed tablet/capsule content ranging from −83% to +478% of the label and even detectable serotonin in some products. ^[16] CDC reports add a sobering epilogue: unsupervised ingestions by young children have surged, with thousands of ER visits in 2019–2022, often involving flavored products. Store securely and treat it like a medicine. ^[17][18]

How to use the signal wisely

• Think timing first. For jet lag, take melatonin at your target local bedtime starting on arrival and for a few nights. For shifting a delayed schedule, smaller, earlier doses can work better—hours before your current sleep time—ideally planned with a clinician and, when possible, paired with morning light. ^[4][7]
• Keep doses modest. Physiologic-range doses (~0.3–1 mg) often suffice for circadian shifting; more isn't necessarily better and may linger into morning. ^[7]
• Separate from food. Avoid taking melatonin within several hours of carbohydrate-rich meals; don't combine it with late dinner. ^[5][12]
• Choose vetted products. Favor brands with third-party testing (e.g., USP/NSF) and avoid "extra-high-dose" gummies, especially around kids. The labeling literature shows why. ^[15][16]

On the horizon: melatonin inside the cell

For decades we thought of melatonin as a bloodstream courier from the pineal. New work suggests many cells may also make melatonin locally—inside mitochondria, the cell's power plants—which may help them weather oxidative stress. Intriguingly, mitochondrial membranes even host melatonin receptors, hinting at a tight local feedback system. It's an early but expanding frontier that could explain some of melatonin's tissue-protective effects seen in models. ^[20][21]

A final thought for modern nights

Melatonin is not a sledgehammer; it's a map. Used with light exposure, regularity, and smart timing, it can guide your internal night to the right place on the clock—remarkably helpful on airplanes and for out-of-sync body clocks. But when we mistake a signal for a sedative, we risk grogginess, glucose mischief, and dosing roulette. Respect the message of darkness, and it will usually return the favor.