SUPPLEMENT SCIENCEInsights
Search

Search Insights

Try choline, nano-curcumin or probiotics.

    Ingredient guide · Ingredient reference

    Does melatonin cause gynecomastia?

    Gynecomastia has been reported in connection with melatonin, but the reviewed evidence does not establish a common or predictable causal effect. A published report is a signal to consider, not a way to calculate your risk. New breast enlargement, a lump, discharge or persistent pain should be assessed.

    Read the evidence ↓

    Supplement Science Insights Editorial Team

    Published September 23, 2026

    A reported case is not a frequency estimate

    A review of melatonin biology mentions one published case of gynecomastia during short-term use. This is a secondary account, not an independently reviewed original case in this article. It cannot show how often the event occurs, exclude other causes or establish that melatonin generally causes breast growth. [1]

    Hormone mechanisms cannot settle the question

    Melatonin interacts with reproductive signaling in experimental research, but human effects remain incompletely understood. It is not valid to move directly from an animal hormone response to a prediction of male breast enlargement at a retail sleep dose. [2]

    Several other causes need consideration

    NHS lists puberty and aging-related hormone changes, excess weight, certain medicines, anabolic steroids and conditions affecting the thyroid, liver or kidneys among causes. The appropriate investigation depends on symptoms and history, not simply whether a supplement was used. [3]

    Bring the timing and product details

    Imagine a person notices tender breast enlargement after starting melatonin. Arrange assessment and bring the supplement and medicine list. A lump, persistent pain, nipple discharge or skin changes should not be dismissed as a harmless expected supplement effect. [3]

    Hypothetical example — interpret a suspected reaction
    EvidenceAppropriate conclusion
    Single case mentioned in reviewPossible signal
    No reliable incidenceRisk cannot be quantified
    Multiple possible causesClinical assessment matters
    New breast changeDo not self-diagnose
    Does melatonin cause gynecomastia? — original article outline diagram
    Original editorial diagram of this article’s sections; no product photograph or clinical finding is depicted.

    Sources for this article

    1. Extrapineal melatonin: sources, regulation, and potential functions - PMC
      Source consulted: 2026-09-21. This is a reference resource, not a claim that we conducted the studies or tested a product.
    2. Melatonin biosynthesis and regulation in reproduction.
      Source consulted: 2026-09-21. This is a reference resource, not a claim that we conducted the studies or tested a product.
    3. Gynaecomastia - NHS
      Source consulted: 2026-09-21. This is a reference resource, not a claim that we conducted the studies or tested a product.