CoQ10 is like a vitamin - we have it naturally in the body and it is not known to have side effects, but has been shown to have many benefits. If you were taking a statin as the same time, it could have been that making you feel bad. Supposedly, COQ10 helps make the statin pain less. I have been experiencing more pain in my joints with cold, damp weather so I don't want to take the Zetia yet as I would think that was what was causing it. Once I level off, I'll give it a go.