system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why aren’t medication dosages based on weight?

Maybe some are. But I’m thinking of simple things like aspirin or Tylenol. Also my blood pressure and cholesterol meds. It seems the only factor is child versus adult. But if I am a large person in pain, why isn’t it appropriate to add an additional pill?
gpt
They are, when a person's weight will make a medical significance.

Most common medication dosages, though, are just fine as is regardless of weight.  Because most people fall within a certain weight range.  If someone is outside of that range, or the medicine is that specific, then the dosage will be changed as needed.