Why does any active chemical in the body, be it drugs or anesthesia eventually leave the body? Why can’t they last forever?

Question

If you any active chemical in your system that alters the homoestasis, why does this chemical eventually leave the body? What prevents it from staying in the body forever?

In: Biology

Answer 1

Theoretically they do last forever. Since we use a drug’s half-life to determine it’s absorption and excretion, the concentration in your body would approach zero, but never reach it. That’s theoretical though, Usually a drug is considered fully eliminated after 4 or 5 half lives