Isoniazid is a drug used in the treatment of tuberculosis and is available worldwide as an inexpensive treatment. Although it is a relatively cheap treatment that is available worldwide, it has a host of adverse reactions which could be serious to deal with. This can make taking Isoniazid a risk for health in some people. The most problematic side effects for people can be very dangerous. Aside from the potential help that this drug can provide for tuberculosis, it can also be dangerous to sensitive individuals.

The common reactions are rashes, abnormal functioning of the liver and hepatitis. Other ill side effects can include sideroblastic anemia, high anion gap metabolic acidosis, peripheral neuropathy, mild central nervous system effects, and many different drug interactions resulting in increased phenytoin or disulfiram levels. This can also lead to epileptic seizures which are uncontrollable. Headache, poor concentration, weight-gain, poor memory and depression are usually side effects of isoniazid use. Patients with suicidal thinking should avoid the use of Isoniazid because it may increase these thoughts.

Peripheral neuropathy occurs when using Isoniazid in people who have neuropathy due to diabetes, uremia, alcoholism, malnutrition, HIV-infection as well as pregnant women. Those with a seizure disorder may also need a vitamin B6 supplement to help prevent seizures and replace the depletion of the vitamin during the course of Isoniazid.

Hepatotoxicity and liver damage can be avoided with close clinical monitoring of the patient. Symptoms which can provide clues to hepatotoxicity will include nausea, vomiting, abdominal pain and appetite increase. These can help to prevent severe painful and potentially fatal side effects from liver damage. Isoniazid is metabolized by the liver mainly by acetylation and dehydrazination which could cause overworking of the liver. Keeping properly hydrated can help to better process the Isoniazid during its use.