Melatonin leaves your body very quickly, usually within about an hour whether you swallow it or get it through an IV. Because it clears out so fast, you'd need to take it often or use a special slow-release version to keep its effects going.

This means that no matter whether you take melatonin as a pill or get it through an IV, your body clears it out at the exact same speed once it's in your blood. The way you initially get the supplement into your system doesn't change how long it stays in your body.

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.

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.

Taking a 10 mg melatonin pill by mouth gets absorbed into your bloodstream very quickly, usually peaking in about 40 minutes. This fast absorption is why doctors recommend taking it about 45 minutes before you want to feel its effects.

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.