That's what happened to me when I took it the day of each tooth filling removal.
The dentist wouldn't take out my metal fillings unless I allowed him to give me anesthesia. Ended up he had to give me several shots because it wouldnt set in.
After that I made sure to take it only directly AFTER succeeding dental visits.
The naturally derived Vitamin C with bioflavonoids worked very well for me in detoxing any anethesia side effects.