The main adverse reactions to isoniazid are peripheral neuritis and hepatotoxicity, and individual patients may experience optic neuritis, fever, rash, decreased blood counts, and gynecomastia. The more common adverse reactions to isoniazid include peripheral neuritis, in which patients may experience unsteady gait, numbness and pins and needles sensation, and finger pain, as well as hepatotoxicity, in which patients may experience dark-colored urine, yellowing of the eyes or skin, nausea, and vomiting. Less common adverse reactions to isoniazid include blurred vision, sometimes combined with symptoms of optic neuritis such as eye pain, as well as fever, rash, decreased blood counts, and gynecomastia. Isoniazid is an anti-tuberculosis medication that is used clinically to prevent various types of tuberculosis and, when used in combination with other anti-tuberculosis medications, to treat various types of tuberculosis such as tuberculous meningitis and other mycobacterial infections. When using isoniazid, it should be noted that patients with abnormal liver function, psychosis, epilepsy and so on cannot use it. It is recommended that patients consult a professional doctor in detail before using isoniazid and follow the doctor’s instructions to avoid adverse consequences.