Those who drink too much coffee may suffer from anxiety, muscle spasms and audio illusions. Prolonged use over time has also lead to osteoporosis, notes the National Osteoporosis Foundation.
By drinking too much coffee, a person may also experience heartburn, stomach discomfort and diarrhea. Coffee has been proven to increase stomach acid when consumed on an empty stomach and acts as an irritant to your stomach lining and the lining of a person's small intestines, as Health Ambition states. Kidneys also have a hard time retaining calcium, magnesium and zinc due to the low iron absorption rate caused by heavy coffee use.