I have recently been prescribed a combination of butalbital and acetominophen for my migraines and tension headaches. I cannot find the difference between half life and overall duration of the drug's effects on the net. from what i understand, the half life of a drug (if it is relatively long) continues to affect the patient in a somewhat subtle way even after the drug's main effects wear off. My question is: what is the difference between half life and overall duration of main effects? Also, what is the main duration (not half-life) of my butalbital, and i would ask that you elaborate on the difference between half-life and overall duration of a drug