The active ingredient stays in your system for up to 2 weeks ( could be less depending on the medication, one would have to read the medication insert (that super long page of tiny print ). However that is in no way saying you should skip a daily regimen based on that information. The protection of the active ingredient dilutes as the time passes so at the end of the 2 weeks its practically nil. If you miss a dose but take it immediately the next day, you would be ok because your still keeping the active ingredient in your body boosted.