Half Life of Medicine Tool

Enter a half life and one or more doses to see the concentration over time using exponential decay

images/half-life.js

Note: this is only a simple mathematical model and medicines can be very complicated. It doesn't account for absorption time, secondary effects, and so on.

Wrap

Wrap assumes the medicine has been taken at the same period for several cycles, so previous doses are still in the system.

Half Life

Imagine you take 100 mg of a medicine. If its half-life is 4 hours, it means that every 4 hours the amount of medicine in your body is cut in half:

Start: 100 mg
After 4 hours (1 half-life): 50 mg
After 8 hours (2 half-lives): 25 mg
After 12 hours (3 half-lives): 12.5 mg

We call this exponential decay.

A common mistake is thinking that a medicine is completely gone after two half-lives. But it doesn't work that way!

After one half-life, ½ is left. After two half-lives ½ × ½ = ¼ is still left. The amount keeps halving, and in theory never quite reaches zero.

Try it yourself: Set the half-life to 6 hours and add a dose of 200 mg. Look at the graph: what's the concentration after 6 hours from the dose time? What's it at 12 hours?