Taking 5 mg of melatonin every night is not proven safe for indefinite use. For most healthy adults, 5 mg taken occasionally or for a short period is generally well tolerated, but 5 mg may be more than you need. Research on continuous, long-term use remains limited.
| Situation | Practical guidance |
|---|---|
| 5 mg occasionally | Usually tolerated by healthy adults |
| 5 mg nightly for a few weeks | Often reasonable, but monitor for side effects |
| 5 mg nightly for months or longer | Discuss regular use with a doctor or pharmacist |
| It causes morning drowsiness | Consider stopping or asking about a lower dose |
| It does not improve sleep | Do not keep increasing the dose. Investigate the cause of insomnia |
What are the risks of taking 5 mg of melatonin nightly?
Taking 5 mg of melatonin can cause:
- Daytime sleepiness or morning grogginess
- Headache
- Dizziness
- Nausea
- Vivid dreams or nightmares
Most reported side effects are mild. However, a systematic review found that longer-term studies were scarce, and a review of higher doses found more reports of drowsiness, headache and dizziness.
Do not drive or operate machinery if melatonin makes you drowsy. Avoid combining it with alcohol, cannabis, sleeping pills, opioids or other products that cause sedation. These combinations can increase sleepiness and reduce alertness.
Is 5 mg more effective than a lower dose?
Not necessarily. Higher doses do not reliably produce better sleep and may increase next-day drowsiness. Melatonin mainly acts as a signal for the body's internal clock, so when you take it may matter as much as how much you take.
Use the lowest dose that provides a clear benefit rather than taking 5 mg automatically. If 5 mg helps you sleep but leaves you groggy, ask a healthcare professional whether a lower dose or different timing would be appropriate.
Who should ask a clinician before taking melatonin?
Speak with a doctor or pharmacist before using melatonin nightly if you:
- Are pregnant, trying to become pregnant or breastfeeding
- Are under 18
- Are over 55 or prone to falls
- Have epilepsy, an autoimmune condition, liver disease or kidney disease
- Take warfarin or another blood thinner
- Take antidepressants, benzodiazepines, opioid pain medicines, seizure medicines, blood-pressure medicines or other sleep medicines
Melatonin can interact with several medicines, including warfarin, fluvoxamine, some antidepressants, seizure medicines, blood-pressure medicines and sedatives.
What if you need melatonin every night to sleep?
Needing melatonin most nights for more than a few weeks is a reason to assess the underlying sleep problem. The American Academy of Sleep Medicine recommends against using melatonin as a routine treatment for chronic insomnia in adults because evidence for its effectiveness and safety is limited. Cognitive behavioral therapy for insomnia, or CBT-I, has stronger support as a long-term treatment.
Melatonin may be more useful for circadian-timing problems, such as jet lag or a delayed sleep schedule, than for persistent insomnia related to anxiety, pain, sleep apnea, restless legs syndrome or irregular sleep habits.
Bottom line
If melatonin has become a nightly habit, review the dose, timing, other medicines and possible cause of poor sleep with a healthcare professional. U.S. melatonin supplements are regulated less strictly than prescription drugs, so the amount in a product may not always match its label.