As with any medication, Jantoven may cause side effects in patients. The most frequently reported adverse reactions are minor and include nausea, gas, loss of hair, vomiting, bloating, and abdominal pain. Some more serious side effects that need to be reported immediately to a physician include the following symptoms: discolored skin, purple fingers or toes, severe pain in the back or sides, a drop in fever, loss of appetite, jaundice, darkened urination, abnormal bruising or bleeding, blood from the noses or gums, abrupt spells of pain or weakness, bloody urination or stools, severe flu symptoms, loss of equilibrium, or impaired vision.