Cyanocobalamin is available in generic form. Common side effects of Cyanocobalamin include injection site reactions (pain, redness, swelling, irritation), diarrhea, nausea, upset stomach, itching, rash, headache, dizziness, weakness, numbness or tingling, fever, joint pain, or a feeling of swelling all over the body.ess serious side effects may include: 1  headache, dizziness, weakness; 2  nausea, upset stomach, diarrhea; 3  numbness or tingling; 4  pain, swelling, redness, or irritation where the injection was given;