Why does coffee make you nauseated?

Coffee is very acidic, so it does give a lot of people stomach problems, like nausea and diarrhea. Some companies offer low-acid coffee grounds (but I personally think they taste awful). If you still need your morning caffiene fix, you could try drinking green tea, which has MORE caffiene than coffee, as well as L-theanine, an amino acid which helps your body absorb the caffeine more regularly--so no more energy crashes!