Hi Dr. Samuel. N. Grief, I am trying to conceive and although late for my period, tested negative with a home pregnancy test. I was surprised to read that antihistamines can cause false negative results so am wondering if NyQuil would fall into this category of causing a false negative? I plan to discontinue use of Nyquil and test again in a few days if I don t get my period but am wondering how common an occurrence this is? Thanks!