I've just developed a cold and went to the store last night to buy OTC cold medicine. I bought a box containing both Vicks DayQuil and Nyquil (for nighttime relief). The box has drug facts for both products, since they have different formulations. Before taking two of the NyQuil capsules, I used an online drug interaction site to check for problems with that and Levothyroxine. The checker reported no known adverse interactions, so I took the pills. I didn't feel the need to take any of the daytime capsules today (although I might another day if my symptoms get worse), but while looking at the box I saw that under the heading “ask a doctor before use if you have …,” thyroid disease was one of the conditions listed for Dayquil, although not for NyQuil. Both products contain acetaminophen and dextromethorphan, but the Dayquil also contains Phenylephrine, while the NyQuil substitutes Doxylamine Succinate. Is this anything to be concerned about?