The oral use of cyanocobalamin may lead to several allergic reactions such as hives; difficult breathing; swelling of the face, lips, tongue, or throat.

SIDE EFFECTS: Call your doctor or seek medical attention right away if you are having any of these side effects: skin rash, hives, or itching; wheezing or trouble breathing; swelling of the face, lips, or throat.

Chewing fresh feverfew leaves can cause mouth sores; swelling of the mouth, tongue, and lips; and loss of taste.

Get emergency medical help if you have signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Other symptoms: Facial or generalized redness ("flushing"), hives (urticaria) on smaller or larger parts of the body, swelling of the eyelids, lips or other parts of the face, itching of the eyes or of the skin in general, hay fever symptoms in the eyes and eczema.

Get emergency medical help if you have any of these signs of an allergic reaction: nausea, vomiting, sweating, hives, itching, trouble breathing, swelling of your face, lips, tongue, or throat, or feeling like you might pass out.

The symptoms affect different areas of the body and include rashes, swelling of lips and throat, difficulty breathing, a fall in blood pressure and eventually loss of consciousness.

Get emergency medical help if you have any of these signs of an allergic reaction (which may occur up to 17 days after you receive the shot): hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

While the symptoms can be dramatic and nasty - fever, rash, red eyes, swelling of hands and feet, swollen lymph glands, inflamed mouth, lips and throat and peeling skin - many patients do not exhibit all, or even most, of them.