What Causes Stomach Cramps And Blood In Stool After Taking Cipar For Migraine?

my daughter was prescribed ciplar la 40 containing propranalol for migraine treatment, she seems to have side effect like , stomach cramps and bloody stools , on checking up with doctor he says the drug will not have such side effect ,advised to go visit a general surgeon.she used some other medicine for migraine prescribed by another doctor who also refused to acknowledge the side effect of nasuea caused by it. I wonder are the side effects well documents , do doctors will have the thorough knowledge of the side effects ? on web search I am finding some effects where as doctor is in denial mode ! we are unable to make out the truth , pls suggest what to do under these circumstances