Melatonin Side Effects
Melatonin is generally safe with minimal serious adverse effects, but commonly causes mild side effects including headaches, somnolence, dizziness, gastrointestinal upset, and daytime drowsiness. 1
Common Side Effects (Mild to Moderate)
The most frequently reported adverse effects from clinical trials include:
- Headaches (0.74% incidence) 2
- Daytime sleepiness/somnolence (1.66% incidence, most common) 2
- Dizziness (0.74%) 2
- Gastrointestinal upset (nausea, general GI disturbance) 1
- Sleep-related adverse events (0.74%) 2
These effects typically resolve spontaneously within a few days without dose adjustment, or immediately upon discontinuation 2. The American Academy of Sleep Medicine guidelines note that short-term use of ≤10 mg daily appears safe in healthy adults 1.
Dose-Dependent Effects
Higher doses (above typical chronobiotic doses) increase the risk and severity of side effects 1:
- At higher doses: hypotension, hypertension, exacerbation of alopecia areata
- Effects reported at lower doses in patients with preexisting conditions
- Optimal dosing appears to be 4 mg/day for sleep promotion, with diminishing returns beyond this 3
Serious or Clinically Significant Concerns
Cardiovascular and Metabolic
- Blood pressure changes (both hypotension and hypertension reported) 1
- Impaired glucose tolerance in healthy women following acute administration 1
Psychiatric
Special Populations Requiring Caution
Exercise extreme caution or avoid in:
- Patients taking warfarin (drug interaction concerns from WHO case reports) 1
- Patients with epilepsy (case reports of adverse effects) 1
- Children/adolescents - concerns about growth hormone regulation (10 mg dose) and reproductive development (3 mg dose), though one study found no differences in pubertal development over ~3 years 1
- Women of reproductive age - National Academy of Sciences recommends caution 1
- Pregnant and breastfeeding women - should not use due to lack of safety data 4
Long-Term Safety Profile
Long-term safety data remains limited, particularly for pediatric populations 1. However:
- A 28-day trial with 10 mg melatonin showed no adverse effects on sleep, clinical labs, or subjective events 1
- Meta-analysis of trials ≤3 months (>200 subjects) reported few adverse events 1
- Pediatric follow-up study (mean ~4 years, doses up to 10 mg) detected no serious adverse events, with 65% continuing daily use 1
- One study raised concerns about potential pubertal delay with very long-term use (>7 years) 5
Critical Safety Considerations
Product Quality Issues
Melatonin is a dietary supplement, not FDA-regulated medication 1. This creates concerns about:
- Purity of preparations
- Reliability of stated doses
- Recommendation: Use United States Pharmacopeial Convention Verified formulations 1
Overdose
A case report of 900 mg overdose (with concurrent alprazolam) resulted in extreme drowsiness and minimal responsiveness, but the patient recovered with supportive care within 32 hours 6. This demonstrates low acute toxicity potential but emphasizes the need for proper dosing.
Specific Population Guidance
Elderly with Dementia
Avoid melatonin in older adults with dementia and irregular sleep-wake rhythm disorder - evidence shows no benefit on total sleep time and potential detrimental effects on mood and daytime functioning 1.
Children with ADHD/Psychiatric Comorbidities
Generally well-tolerated at 3-5 mg doses, though non-serious adverse events are more common than placebo (RR 1.56) 5. Benefits may outweigh risks with appropriate informed consent 1.
Timing and Administration Considerations
Optimal timing is 1-2 hours before desired bedtime (approximately 6 PM for typical sleep schedules) to minimize daytime somnolence and maximize efficacy 7, 3. Administration too close to bedtime or at inappropriate times can increase drowsiness-related adverse effects 8.