It depends on the half-life of the pill and how much you are taking. Sometimes it will stay in your system for a week, sometimes only 24 hours.

I have heard that even medications that are effective, they have a placebo effect to a degree. The more confident you are in the pill you are taking, generally means better results. If you feel guilty about not taking the pills it could make you feel worse than what you really are.

Doggiedo has a really good suggestion. If you take your pills at the same time everyday it is easier to take them. Or put them in a place that is visible that you might pass a few times a day so it will be on your mind. Or get one of those things where you put your daily amount of medication in for all the days of the week. If you don't take it, you will know.