Thanks for your question on "Ask The Doctor".
There no drug interactions found if NyQuil and Mucinex D are taken together.
On the other hand they will be helpful to relieve your symptoms if taken together.
It is always better to consult your doctor and then take medicines.
Wish you a good health.
These Q&A’s are for educational purposes and should not be relied upon as a substitute for medical advice you may receive from your physician. If you have a medical emergency, please call 911. These answers do not constitute or initiate a patient/doctor relationship.