People with severe liver disease (cirrhosis) have trouble making and clearing melatonin, which changes how much of this sleep hormone is in their bodies. This happens because the damaged liver can't process or produce the hormone properly.

People with severe liver disease make about half as much of the sleep hormone melatonin as healthy people do. This happens because a damaged liver struggles to help the body make or control this important chemical.

When you swallow melatonin, your liver breaks down a large portion of it before it can enter your bloodstream. Because of this, you need to take a much larger pill to get the same amount of the hormone in your system as you would from an injection.

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.