The most common dosage of melatonin supplement that you can buy is 3mg. But there are instances where 3mg is just not enough. Our body responds differently to melatonin and we may need more or less depending on our genetic make up. The amount of melatonin we need also depends on the severity and the type of health condition that we want to treat. 10 mg of melatonin is ideal for those persons suffering from severe insomnia. Before taking high doses of melatonin, consider other factors that can make your sleep difficult. Spikes in blood sugar at night and caffeine are some factors that make sleeping at night difficult. Melatonin dosages in the range of 10-50mg are typically used in cancer treatment and in the treatment of other health conditions.