A 5 mg dose of immediate-release melatonin is usually noticeable for about 4 to 8 hours. Sleepiness is often strongest during the first few hours, but some people feel groggy the next morning. The duration depends on the product type, age, metabolism, other medicines and whether the tablet is immediate-release or extended-release.
5 mg Melatonin at a Glance
| Question | Typical answer |
|---|---|
| When does it start working? | About 30 minutes to 2 hours |
| When is the effect strongest? | Usually during the first few hours |
| How long can the sleep-promoting effect last? | Roughly 4 to 8 hours |
| How long is melatonin's half-life? | Approximately 30 to 60 minutes |
| Can it cause next-day drowsiness? | Yes, especially in some people and older adults |
Why Does Melatonin Last Longer Than Its Half-Life?
Melatonin can continue promoting sleep after its blood level starts to fall. After an oral immediate-release dose, melatonin reaches peak blood levels at about 50 minutes. Its blood half-life is usually 30 to 60 minutes, but that does not mean its effects stop after one hour.
Research on oral melatonin has found that levels may return toward baseline within about 4 to 8 hours. The timing varies by study and formulation. Immediate-release melatonin generally acts for less time than slow-release or extended-release products.
Immediate-Release Versus Extended-Release Melatonin
- Immediate-release 5 mg melatonin: Usually helps with falling asleep and may have noticeable effects for about 4 to 8 hours.
- Extended-release melatonin: Releases melatonin more gradually and is designed to continue working through more of the night. It may last longer than an immediate-release tablet, but the duration varies by product.
- Gummies, liquids and chewables: These may absorb differently from tablets, so the timing can vary.
Check the label for terms such as immediate-release, extended-release, sustained-release or prolonged-release.
Why Can 5 mg Melatonin Still Make You Tired the Next Day?
Melatonin can cause next-day drowsiness even when its blood levels are falling. Morning tiredness is more likely if you:
- Take melatonin late at night
- Sleep fewer than 7 to 8 hours
- Use an extended-release product
- Are older, since melatonin may remain active longer with age
- Combine melatonin with alcohol, cannabis or other medicines that cause sleepiness
Headache, dizziness, nausea and sleepiness are reported side effects. Do not drive or operate machinery if you feel drowsy, dizzy or unable to concentrate.
What Should You Do After Taking 5 mg?
Do not take another dose the same night just because you do not feel sleepy yet. Melatonin can take 1 to 2 hours to work, depending on the product and the person. Follow the product label or your clinician's instructions.
Avoid alcohol and other sedating medicines unless a doctor or pharmacist has confirmed that the combination is appropriate. Ask a healthcare professional before using melatonin if you take warfarin, seizure medication, antidepressants, sleeping pills or other regular medicines.
If someone cannot be awakened, has trouble breathing, collapses or has a seizure, call 911. For a suspected overdose or accidental ingestion in the United States, contact Poison Control at 1-800-222-1222.