Half life plays a role in medications we take too, for example, my mom takes Lisinopril (A.C.E. inhibitor to lower blood pressure) I took one by mistake one time, doc said not only does it get along with the few meds I take, it's half life is only 12.5hrs. Medications are are at their peak efficiency when most of their ingrediencies are working together to give yo the pest Their half life is considered when the ingrediencies are only working half potential. So bottom line if a medication has 6hr half life, it should affect you for appx 6 hrs, and take aapx 12 h for it to be out of your system.;