Melatonin does interact with several hormones in your body, but for most adults taking standard doses short-term, the effects appear minor and reversible. The bigger concern is dose: most store-bought melatonin supplements contain 3 to 10 mg, which is roughly 10 to 25 times higher than what your body naturally produces at night. At these levels, melatonin can temporarily influence prolactin, insulin, growth hormone, and reproductive hormones, though the clinical significance for healthy adults remains small.
What Counts as a Physiological Dose
Your body’s natural melatonin peak at night produces blood levels around 30 to 60 pg/ml, depending on your age. In a controlled trial of older adults, even a “low dose” supplement of 0.4 mg pushed blood levels to around 405 pg/ml, roughly 10 times higher than normal nighttime peaks. A 4 mg dose, which is closer to what you’d find on store shelves, produced levels near 4,000 pg/ml. That’s almost 100 times higher than what your brain releases on its own.
This matters because melatonin isn’t just a sleep signal. It acts on receptors throughout the body, including in the pituitary gland, pancreas, and reproductive organs. The higher the dose, the more likely you are to see effects beyond sleep timing.
Prolactin Goes Up
One of the most clearly documented hormonal effects is a rise in prolactin. In a study published in Pediatric Research, participants who received melatonin saw their blood levels spike to more than 1,000 times above baseline. Their prolactin levels increased, while testosterone and the reproductive hormones LH and FSH stayed the same. Prolactin is the hormone responsible for milk production, but in both men and women, persistently elevated levels can suppress sex drive and interfere with ovulation or sperm production.
For occasional use, a temporary bump in prolactin is unlikely to cause noticeable symptoms. But if you’re taking melatonin nightly for months, the cumulative effect on prolactin is worth considering, particularly if you notice changes in libido or menstrual regularity.
Growth Hormone Gets a Boost
Melatonin has a mild stimulatory effect on growth hormone. In one trial, oral melatonin roughly doubled the growth hormone release triggered by the body’s natural signaling pathway. This isn’t necessarily harmful. Growth hormone peaks naturally during deep sleep, and melatonin may simply amplify that existing process. For most adults, this effect is neutral or even favorable, since growth hormone supports tissue repair and metabolism. In children, the picture is more complicated, as any amplification of growth hormone signaling during development could theoretically influence growth patterns, though no studies have confirmed this as a problem.
Insulin and Blood Sugar
Melatonin reduces insulin secretion from the pancreas. This is well established in both lab and human studies, and it’s actually part of why eating late at night (when melatonin is naturally rising) can worsen blood sugar control. Your body is essentially saying: it’s nighttime, stop processing food.
Interestingly, when melatonin was given before an evening meal in healthy men, it improved glucose tolerance and insulin sensitivity while lowering post-meal blood fat levels. The hormone seems to help your body handle food more efficiently in the evening, as long as you’re not eating right at bedtime when melatonin levels are at their highest. If you have diabetes or prediabetes, the timing of your melatonin dose relative to meals could matter more than the dose itself.
Thyroid Hormones Appear Unaffected
A pilot study in healthy active men found that a single dose of melatonin had no effect on TSH, free T4, or the thyroid’s response to exercise. Both the melatonin and placebo groups showed identical thyroid hormone patterns. While this is only one small study, it aligns with the broader clinical picture: there’s no strong evidence that melatonin disrupts thyroid function in adults.
The Puberty Question in Children
This is where the concern is most active. Melatonin levels naturally decline as children approach puberty, and some researchers have worried that supplementing melatonin could interfere with that decline and delay sexual development. A 2023 systematic review in eClinicalMedicine, published by The Lancet, examined the evidence across 22 randomized studies involving 1,350 pediatric patients. Three studies found little or no influence on pubertal development after 2 to 4 years of treatment. One study flagged a potential delay after more than 7 years of continuous use.
A separate long-term follow-up of children treated for an average of 3.1 years with doses ranging from 0.3 to 10 mg found no significant difference in puberty development, social development, or mental health compared to the general population. However, in a longer follow-up averaging 7.1 years, 31% of parents reported subjective concerns about delayed puberty onset, compared to 17% in the general population.
Adding to the biological plausibility, a case-control study of teenage boys with naturally delayed puberty found that their melatonin levels were significantly higher than those of age-matched peers, and melatonin correlated negatively with testosterone and FSH. This doesn’t prove supplementation causes delays, but it suggests that higher melatonin during adolescence is at least associated with later development. The Lancet review rated the overall evidence as “very low certainty” and called the findings speculative, but European drug regulators have listed delayed puberty as a potential long-term risk of melatonin treatment in children.
What Long-Term Use Looks Like
For adults, the reassurance is cautious but consistent. A review in Clinical Interventions in Aging concluded that “the minor effect of melatonin on levels of luteinizing hormone, follicle stimulating hormone, prolactin and growth hormone that have been demonstrated in younger adults are likely to be not clinically significant in older adults.” Melatonin appears to have a favorable safety profile in older populations, though the authors noted a lack of evidence on prolonged use.
The honest summary is that short-term melatonin use at reasonable doses (0.5 to 3 mg) does not appear to cause lasting hormonal disruption in adults. The effects on prolactin and growth hormone are real but modest. The effects on reproductive hormones are minimal at typical doses. Thyroid function seems untouched. The most legitimate concern is in children and adolescents, where years of nightly use could potentially interfere with the natural melatonin decline that precedes puberty.
Keeping the Dose in Check
Most of the hormonal effects scale with dose. If you want to minimize any endocrine impact, a dose of 0.3 to 0.5 mg taken 30 to 60 minutes before bed more closely mimics your body’s natural output. Research consistently shows that these lower doses are just as effective for shifting sleep timing as the 5 or 10 mg tablets that dominate store shelves. Higher doses don’t help you sleep faster; they just flood your receptors and increase the chance of next-day grogginess and hormonal spillover. Starting low also lets you identify your minimum effective dose, which for many people turns out to be far less than what’s printed on the bottle.