Can melatonin cause side effects on hair?

Melatonin is a hormone naturally produced by the pineal gland in the brain. Its most well-known function is regulating the circadian rhythm, that is, the sleep-wake cycle.

One topic that has gained attention is whether melatonin can affect hair health, causing hair loss, weakening, or noticeable changes in texture and appearance.

Could a hormone associated with rest have consequences on something as visible and emotionally sensitive as hair?

Melatonin and hair: A direct relationship or coincidence?

Various users who take melatonin supplements have anecdotally reported hair loss or hair thinning after weeks or months of use. While health forums and personal experiences are not scientific evidence, they have prompted some researchers to explore a potential connection. However, so far, formal studies evaluating the specific side effects of oral melatonin on human hair are scarce.

One of the most frequently cited studies on this topic is that of Fischer et al. (2004), published in the British Journal of Dermatology. This randomized, placebo-controlled pilot trial tested a 0.1% melatonin solution applied once daily to the scalp in 40 women with androgenetic alopecia or diffuse hair loss for six months. Hairs were assessed with trichograms (plucked-hair counts). The share of hairs in the growth (anagen) phase rose in two of four subgroup comparisons; the other two were not significant. The study did not evaluate oral melatonin, and it did not report hair loss as a side effect. It was small and had no long-term follow-up.

This does not mean adverse effects do not exist.

A 2016 review of melatonin safety by Andersen et al., published in Clinical Drug Investigation, found mainly mild side effects with short-term use and did not list skin or hair problems among them.

The side effects it listed were dizziness, headache, nausea and sleepiness. However, clinical trials often do not specifically focus on hair health, so less frequent or subtler symptoms may go under the radar.

The same review advised that pregnant or breastfeeding women should not take melatonin, and said that long-term safety in children and teenagers needs more study. In the UK, melatonin is a prescription-only medicine (NHS). In the US it is sold as a dietary supplement, and the dose on the label may not match the product: a 2017 study of 31 supplements found melatonin content from 83% below to 478% above the labelled amount (Erland & Saxena, 2017). Ask a doctor or pharmacist before using melatonin, especially if you are pregnant, breastfeeding, giving it to a child or taking other medicines.

How can hair loss reports after taking melatonin be explained?

One hypothesis that could explain a possible connection between oral melatonin and hair loss relates to its hormonal interaction.

Although melatonin is not a sex hormone, it influences the endocrine system and could, in theory, alter the hormonal balance in some individuals. For instance, melatonin affects the release of gonadotropins (hormones that regulate ovarian and testicular function). If this delicate balance is altered, some sensitive individuals may experience indirect consequences on the hair follicle cycle, which is responsible for hair growth.

However, this theory has not yet been validated by human studies.

Hair loss is multifactorial: it can be influenced by stress, hormonal changes, nutritional deficiencies, autoimmune diseases, or even disrupted sleep. And since many people take melatonin because they already suffer from insomnia or stress, it is possible that these underlying factors — and not the supplement itself — are responsible for the changes in hair health.

Another aspect to consider is melatonin’s bioavailability. In some people, the body may absorb more or less of the supplement, and its liver metabolism may vary. Therefore, an excess in melatonin plasma concentration could, in isolated cases, dysregulate certain physiological processes, including hormonal ones. But this remains a hypothesis, not a scientific conclusion.

What does it feel like when hair reacts to melatonin?

Anecdotal reports from those who have attributed hair loss to melatonin describe symptoms such as progressive thinning, increased hair left on the pillow or in the shower, and a sensation of hair fragility.

In some cases, people also mention that hair loses volume or looks “dull.” In these accounts, the changes are often said to appear within a few weeks of starting the supplement; no study has described a pattern.

It is important to understand that even if melatonin plays a role in these changes, it would not necessarily be the only factor. Hair health depends on many elements, and the temporal coincidence between starting melatonin and hair loss does not prove causation.

User Experiences

Community feedback provides a nuanced look into how melatonin might affect hair, especially when used as a treatment for hair loss. Several users shared both positive and negative experiences, with a recurring theme being the variability in how individuals respond to topical or oral melatonin.

One user described their experience with topical melatonin, reporting improved hair density after several weeks of use. However, they also noted that the application caused scalp dryness and occasional itching. This was echoed by another user who felt the formula helped reduce shedding but triggered some irritation and flakiness on the scalp.

Some users expressed concerns about the hormonal activity of melatonin, particularly when used long-term. One individual warned about possible hairline skin issues, citing that they developed mild breakouts along the scalp after using a melatonin-based topical solution. They speculated this could be due to the compound’s interaction with their natural hormone levels.

Another user thread included a comment from someone using oral melatonin for sleep who noticed no hair benefit but did experience minor acne flare-ups. They wondered if melatonin’s influence on sleep cycles and hormones could indirectly impact sebum production or skin inflammation.

Despite these side effects, a few users remained optimistic, arguing that the benefits of reduced hair shedding outweighed the relatively mild reactions. A couple of contributors also emphasized that combining melatonin with anti-inflammatory ingredients or rotating it with other topicals significantly reduced the irritation.

Overall, the consensus in community discussions is that while melatonin might offer benefits for hair density or shedding, its side effects—particularly scalp-related—are not negligible. Users commonly reported dryness, itching, or minor acne, suggesting that anyone considering melatonin for hair should monitor their reaction closely.

Evidence lacking, questions remaining

In summary, although some people report hair loss after taking oral melatonin, there are no clinical studies that conclusively support this relationship. The one placebo-controlled trial on melatonin and hair tested topical melatonin as a possible treatment, not as a cause of hair loss. However, it is also true that research on specific side effects on hair is limited. In the absence of broader trials focused specifically on this concern, it cannot be stated with certainty that melatonin causes or does not cause hair loss.

If you notice changes in your hair after starting melatonin, talk to the doctor or pharmacist who advised it before stopping, especially if it was prescribed. They can also discuss other ways to manage sleep problems.

References

• Andersen, L. P., Gögenur, I., Rosenberg, J., & Reiter, R. J. (2016). The safety of melatonin in humans. Clinical Drug Investigation, 36(3), 169–175. [https://pubmed.ncbi.nlm.nih.gov/26692007/]

• Fischer, T. W., Burmeister, G., Schmidt, H. W., & Elsner, P. (2004). Melatonin increases anagen hair rate in women with androgenetic alopecia or diffuse alopecia: results of a pilot randomized controlled trial. British Journal of Dermatology, 150(2), 341–345. [https://pubmed.ncbi.nlm.nih.gov/14996107/]

• Erland, L. A., & Saxena, P. K. (2017). Melatonin natural health products and supplements: presence of serotonin and significant variability of melatonin content. Journal of Clinical Sleep Medicine, 13(2), 275–281. [https://pubmed.ncbi.nlm.nih.gov/27855744/]

• NHS. About melatonin. [https://www.nhs.uk/medicines/melatonin/about-melatonin/]

• FDA MedWatch. (n.d.). Safety Information and Adverse Event Reporting Program. [https://www.fda.gov/safety/medwatch-fda-safety-information-and-adverse-event-reporting-program]