Understanding Melatonin and its Role in Sleep
Melatonin is a hormone naturally produced by the pineal gland in your brain, primarily in response to darkness [1.11.2]. Its main function is to regulate the body's circadian rhythm, also known as the 24-hour internal clock or sleep-wake cycle [1.11.1, 1.11.2]. As light fades in the evening, melatonin levels rise, signaling to your body that it's time to prepare for sleep. These levels peak in the middle of the night and decline as morning approaches, helping you wake up [1.11.4].
When taken as a supplement, exogenous (synthetic) melatonin aims to mimic this natural process [1.11.2]. It is often used to address sleep issues like insomnia, jet lag, or delayed sleep phase syndrome [1.2.5, 1.11.3]. A 5mg dose is a common strength available over-the-counter, although experts often recommend starting with a lower dose of 1 to 3 milligrams [1.9.3, 1.9.4].
The Lack of FDA Regulation
It is crucial to understand that in the United States, melatonin is classified as a dietary supplement, not a drug. This means it is not regulated by the Food and Drug Administration (FDA) with the same rigor as prescription medications [1.8.3, 1.8.4]. Studies have found significant discrepancies between the melatonin content listed on the label and the actual amount in the product, with variations ranging from -83% to +478% [1.4.1, 1.5.1]. Some supplements have also been found to contain other substances, like serotonin, which can cause harmful effects [1.4.1, 1.8.3].
Common Side Effects of Melatonin 5mg
While melatonin is generally considered safe for short-term use, a 5mg dose can cause several side effects. Higher doses are more likely to produce these effects [1.3.5].
Most Frequent Side Effects:
- Daytime Drowsiness: A lingering groggy feeling, sometimes called a 'melatonin hangover,' can occur, especially if the dose is too high or taken too late [1.2.1, 1.3.5]. Don't drive or operate machinery within five hours of taking melatonin [1.2.2].
- Headache: This is one of the most commonly reported side effects [1.2.2, 1.4.5].
- Dizziness: Feelings of lightheadedness or unsteadiness can occur [1.2.2, 1.3.5].
- Nausea: Some individuals experience stomach discomfort or nausea after taking melatonin [1.2.2, 1.3.5].
Less Common Side Effects:
- Vivid dreams or nightmares [1.2.2, 1.3.4]
- Irritability and mood swings [1.2.2, 1.3.4]
- Stomach cramps, diarrhea, or constipation [1.2.2]
- Short-term feelings of depression or mild anxiety [1.3.2]
- Confusion or disorientation [1.2.2]
- Reduced alertness [1.3.2]
Potential Long-Term Risks and Considerations
The long-term safety of daily melatonin use, especially at doses like 5mg, is not well-studied and remains largely unknown [1.4.3]. Some concerns have been raised regarding chronic use:
- Hormonal Effects: There is some concern that long-term use in children and adolescents could interfere with puberty and hormonal development, though human studies are inconclusive [1.2.5, 1.5.1].
- Dementia Risk: One associational study noted that older adults who frequently used sleep aids (both over-the-counter and prescription) had a higher risk of dementia, but could not isolate melatonin as the cause [1.4.1].
- Underlying Conditions: Relying on melatonin for chronic sleep issues might mask an underlying medical condition, such as sleep apnea or a mental health disorder, that requires proper diagnosis and treatment [1.4.3].
Special Populations
Certain groups should exercise particular caution with melatonin:
- Pregnant or Breastfeeding Individuals: There is not enough reliable information to know if melatonin is safe during pregnancy or while breastfeeding; it is best to avoid use [1.6.4, 1.9.3].
- Children and Adolescents: Melatonin should only be used in children after consulting a pediatrician. Doses of 5mg are typical for adolescents, but there are concerns about its effect on development [1.2.5, 1.5.5].
- Older Adults: This group may be more susceptible to daytime drowsiness and an increased risk of falls and fractures [1.4.5, 1.5.1]. Melatonin should be avoided in older adults with dementia [1.4.5].
- Individuals with Autoimmune Diseases: Melatonin can stimulate immune function and should not be used by those with autoimmune disorders [1.2.3, 1.6.1].
Comparison of Sleep Aids
| Feature | Melatonin (5mg) | Prescription Hypnotics (e.g., Zolpidem) |
|---|---|---|
| Regulation | Unregulated by FDA (Dietary Supplement) [1.8.4] | FDA-approved and regulated drug [1.5.4] |
| Mechanism | Supplements natural hormone to regulate sleep-wake cycle [1.11.1] | Acts on brain receptors to induce sleep (e.g., enhances GABA) |
| Common Side Effects | Drowsiness, headache, dizziness, nausea [1.2.2] | Drowsiness, dizziness, impaired motor skills, complex sleep behaviors [1.5.1] |
| Dependence Risk | Unlikely to cause dependence or tolerance [1.2.2] | Can be habit-forming and lead to dependence and withdrawal |
| Availability | Over-the-counter [1.8.1] | Prescription only [1.5.4] |
Drug and Substance Interactions
Melatonin can interact with a wide range of medications, potentially increasing side effects or reducing the effectiveness of other drugs. Always consult a healthcare provider before combining melatonin with other substances.
Key Interactions Include:
- Blood Thinners (e.g., Warfarin): May increase the risk of bleeding [1.6.1, 1.6.5].
- Blood Pressure Medications: Melatonin can affect blood pressure, potentially making these drugs less effective or causing pressure to drop too low [1.6.1, 1.6.3].
- Diabetes Medications: Melatonin can affect blood sugar levels, requiring close monitoring [1.6.1, 1.6.4].
- CNS Depressants (e.g., Benzodiazepines, Alcohol): Combining these can cause additive sedative effects and excessive drowsiness [1.6.1, 1.6.3].
- Contraceptive Drugs: May increase melatonin levels and potential side effects [1.2.3, 1.6.4].
- Immunosuppressants: Melatonin may interfere with immunosuppressive therapy [1.6.1].
- Anticonvulsants: Melatonin might increase the frequency of seizures in some individuals [1.6.1].
Conclusion
A 5mg dose of melatonin can be effective for short-term sleep issues for some adults, but it is not without side effects, the most common being next-day drowsiness, headaches, and dizziness [1.2.1, 1.2.2]. The lack of FDA regulation means product purity and dosage accuracy are significant concerns [1.8.2, 1.8.3]. The long-term safety of daily use remains unproven, and it can interact with numerous medications [1.4.3, 1.6.1]. It is crucial to consult a healthcare professional before starting melatonin, especially for long-term use or for specific populations like children, the elderly, or those with existing medical conditions.
For more information from an authoritative source, you can visit the National Center for Complementary and Integrative Health (NCCIH).
