I don't know if we know that, definitively. All the studies were done on people using it daily, for the recommended use.
However, let's take aspirin as an example. For most people, taking an aspirin occasionally won't have any negative effect. For some, though, taking any anti-inflammatory can cause a whole host of problems, and they may not even know it. Aspirin is a blood thinner, and that can cause problems for some people.