What half-life tells you

Every compound leaves your body over time and half-life is how we measure the speed. The half-life is how long it takes for half of a dose to clear out of your body. Wait one half-life and half remains. Wait another and half of that is gone, so a quarter is left, and so on.

Half-life matters because it decides how often you dose. A compound with a short half-life of a few hours is in and out quickly, so a protocol might call for it once or twice a day to keep a steady level. A compound with a long half-life, like semaglutide at about a week, sticks around so long that you only inject it once a week.

Long half-lives have a second effect worth knowing. The compound does not fully clear before your next dose, so it stacks up over the first several weeks until it reaches a steady level. This is why some compounds take a month or more before you feel much. You are not doing anything wrong. The level is still climbing toward where it will settle.