system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why do some medications require you to take them multiple times a day while others only require a shot every few months?

I was watching a commercial for yet another medication with a ridiculous name and when they got to the dosage instructions it said after two booster shots you only need 4 per year. Usually pills like an aspirin or something like that you take multiple per day.

What is it about some medications that make it able to stay in the body for days or months and why others are gone in hours? Does the actual medicine stay in the body that long or is it expelled sooner and somehow the effects just lasts for months?
gpt
Medications have a half life and effective concentration. The half life is the period that it takes for your body to remove 50% of the drug from your body. 8 hours might be a reasonable half life. And you need a specific minijrmum amount of the drug in your body to work but also not too much because the side effects might to unsafe or unwanted.

Take for example a drug with a half life of 8 hours and you need 5mg of it in your body to work and anything more than 7mg will make you sick. You'd want to take 1.5mg every 3 hours because if you have 6.5mg in your body it takes 3 hours to get to 5mg, and that will be within the targets.