What happens if you use painkillers when you're not in pain?

It is likely that nothing will happen if you ingest Advil and you didn't have any pain; however, you really should not use any pain medication unless you need it. All medications come with possible side effects. Some of the side effects that may occur are (but not limited to) stomach upset (which is why you should always take Advil with food), gastrointestinal bleeding, heart attack and stroke. In addition, if you are allergic to aspirin or are already taking aspirin, you should not take Advil because it can increase your chances of the aforementioned side effects or increase the effects of aspirin.

The bottom line is you should not take any medication unless you need it.