First of all, I have searched extensively for the correct answer online without any luck. The Pill I have is White, Round, Imprint says "M18" and it is scored twice on the back so it can break into quarters. It is definitely NOT Metoprolol 25 mg. Metoprolol is scored once and the imprint has the M over the 18. I also read that it could be Guaifenesin 200 mg, Ephedrine 25 mg, but I can't find an image to confirm that. Do those pills say "M18" and are cross scored on the back to break into quarters? Keep in mind this may be a completely different thing all together being that the medication is old, from 2002, and it may not be domestic for all I know. I have seen a few posts on this similar subject and people are quick to answer Metoprolol which it most certainly is not. Please look into this one with care as I assure you the answer is not easily searched on the web. Thank You.