It's an antibiotic and it is what is prescribed to fight anthrax. It is also very commonly prescribed for UTIs. Any antibiotic can make you feel pretty yucky. I can't stomach Erythromycin (sp?) but didn't have any trouble with Cipro.
If you have problems with Cipro, watch out for Avelox also. Avelox gave me horrible palpatations and nausea and the two drugs have a similar properties.
I was given Cipro for a UTI/Kidney infection a couple of months ago and it made me fell really yucky too but it did work really well for me. And it was very expensive, at least to me. Especially since I don't have insurance right now.