People process melatonin very differently, even when taking the exact same 10-milligram dose. Factors like your genes, metabolism, and body chemistry cause these wide differences, which is why it's so hard to create one-size-fits-all dosage recommendations.

Taking melatonin by injection results in about 110 times more of the drug in your blood compared to taking the same dose by mouth. This happens because your liver breaks down most of the oral melatonin before it reaches the rest of your body, which is why you need a much larger pill to get the same effect as a small injection.

When you take melatonin pills, your body only absorbs about 15% of the dose into your bloodstream because most of it gets broken down before it can circulate. This means oral supplements deliver much less active melatonin to your system compared to an injection.

Animal studies suggest that humans might need 100 to 200 milligrams of melatonin daily to get its protective and anti-inflammatory benefits, which is much higher than the 2 to 10 milligrams usually tested in heart studies. This big difference in dosage might be why past heart research hasn't shown clear results.

When you swallow melatonin pills, your liver breaks down most of it before it can actually enter your bloodstream, meaning only about 2.5% of the dose actually works. Because so much is lost this way, you might need to take much higher oral doses to get the same effect as an injection.

When you take a melatonin pill, your body only absorbs about 15% of it because most of it gets broken down by your liver before it enters your bloodstream. Even so, the amount that does get absorbed can still be up to ten times more than what your body naturally makes at night.