<s>[INST] What are the adverse reactions/side effects of the application of metronidazole gel on the gums by a dentist ? I experienced already metallic taste and mild headaches. Had alcohol the day after the application of metronidazole gel. Am age 64, 180 cm and 82 kg. So far was in good health and am taking no medication. [/INST] Thanks for your query, I have gone through your query.The adverse effects of the metronidazole includes metallic taste, white patches, altered taste. if you take metronidazole along with alcohol, it can cause nausea, vomitting, and stomach pain. so better avoid both together. if you have developped allergic reaction then better stop using the gel. consult your oral physician and get it replaced with other drugs like tetracycline. i hope my answer will help you, take care. </s>