There is no consensus on the best melatonin supplement dosage for adults, but some studies have recommended that the safest and most optimal dose is lower than what most melatonin supplements on the market contain. While doses as high as 10 mg of melatonin are available, higher concentrations are more likely to result in side effects such as drowsiness the next day. One double-blind, placebo-controlled study in adults aged 50 and older found the best results at a dose of 0.3 mg compared to 0.1 mg and 3 mg of melatonin. They concluded based on their research that the lowest, fully effective dose is the wisest choice for normalizing melatonin levels.