it depends on the form of vitamin b12 you are taking. gastrointestinal side effects associated with parenteral cyanocobalamin or vitamin b12 given by injection have included dyspepsia nausea vomiting and mild transient diarrhea. these side effects are very mild or not present at all with oral vitamin b12. if you are experiencing severe gas pains that have not subsided within a few hours you should consult your health-care provider.
can a b12 supplement taken with an antidepressant cause severe gas pains?