What are the side effects of isoniazid?

Mild side effects of isonizid may include: diarrhea; upset stomach; vision trouble. Immediate medical help is needed if any of these less common, serious side effects occur: signs of liver damage, including brown or dark yellow urine, yellowed eyes or skin, vomiting, upset stomach, no appetite or feeling overly tired or weak; signs of a serious allergic reaction, including itching, rash, hives, a tight feeling in the chest, trouble breathing or swollen tongue, lips, mouth or face; signs of low vitamin B6, including a red or sore mouth, cracked corners of the mouth, a scaly rash or feeling irritable or confused; pain or tenderness in the stomach; feeling unusually thirsty or frequent urination; eye pain; painful or swollen joints; tingling or numb hands and feet; fever or chills; sore throat or swollen glands; unusual bruises or bleeding; trouble with memory; mood or mental changes; and seizures.