What happens after a dose

Once you inject a peptide, it goes on a short journey. Knowing the rough shape of it explains a lot of the rules you will follow later.

First it has to get in. Most peptides are injected just under the skin, into the fat layer, which is called subcutaneous (sub-kew-TAY-nee-us). From there, the compound seeps into your bloodstream over minutes to hours. This is also why you rarely swallow a peptide. Your stomach would digest it like food before it ever reached your blood.

Next, it travels and does its work by fitting the receptors it was shaped for, the way we covered in the last lesson.

Then your body breaks it down. Peptides are made of the same amino acids as your food, so your body dismantles them with the same tools and clears the pieces, often through the kidneys. That is why most peptides do not linger for weeks the way some drugs do and it is why half-life matters.

You do not need the textbook version of this for now, just the shape. It gets in slowly through the fat, works for a while, then gets taken apart and cleared.