Melatonin is generally considered safe when used in small doses, but taking too much can increase the chance of side effects. For many adults, doses around 5 to 6 mg per day or less are commonly described as safe. Higher amounts, especially above about 10 mg, are more likely to cause unwanted effects even though serious toxicity is uncommon.
When melatonin is taken in larger doses, people may experience symptoms such as excessive sleepiness, headaches, dizziness, or feeling groggy the next day. Research comparing different dose ranges shows that higher doses tend to increase these mild side effects without clearly improving sleep benefits. In other words, taking more does not always make the supplement work better.
Very large doses have been studied and even reported in overdose cases, and most people mainly develop strong drowsiness and temporary symptoms. However, safety data for long term use at high doses is limited, and the risk may increase when melatonin is combined with other medications that affect the brain or cause sedation.
If sleep problems continue or if you feel the need to increase the dose regularly, it is best to speak with a doctor or pharmacist before adjusting the amount you take.