You should not take cyanocobalamin-based products if you: Have a known cobalt allergy Have Lebers hereditary optic neuropathy , as B12 can worsen vision in this condition Discuss nasal B12 with your clinician first if you have: Severe megaloblastic anemia Polycythemia vera or other bone marrow disorders Low iron or folate Kidney disease Are undergoing chemotherapy or using bone marrow-suppressing drugs Are pregnant or breastfeeding Possible Side Effects Most side effects reported with B12 nasal products are mild and temporary: Slight nasal irritation, burning, or dryness Runny or stuffy nose, sneezing, or sore throat Mild headache Nausea or a brief metallic taste Tingling or pins and needles sensations, especially early on as nerves recover Serious reactions are rare but require immediate medical care: Rash, hives, or intense itching Swelling of the face, lips, tongue, or throat Trouble breathing or swallowing Fever, chills, or signs of infection that dont match a simple cold If anything feels out of proportion or youre unsure, stop the product and speak with your healthcare provider or seek urgent care

Front Physiol 2013
There is no treatment that is completely effective at removing all impacts on mucus and infection, however, and so research continues on several different classes of therapeutics targeting mucus and its pathogens
In most cases, this resolves on its own
El-Sayed M, Ali N, Ali Z
Proper diagnosis and treatment provide important benefits, including: Who May Be a Candidate for BPC-157 Therapy