Hi. I've just googled this and yes, diarrhoea is top of the list of possible side effects, along with nausea. It can also cause constipation so in effect, it could make you feel as though you have IBS. I think the side effects should diminish after a while once your body adjusts. My mum takes Citalopram for depression/panic attacks. She always seems to be constipated - maybe it is the drug or perhaps its just being 88 years old and having funny bowels!