Isoniazid Side Effects: What You Need to Know

If you or someone you know is taking isoniazid for tuberculosis, the drug’s benefits are clear— it kills the bacteria that cause TB. But like any medication, it can bring unwanted reactions. Knowing what to expect helps you stay ahead of problems and keep treatment on track.

Common side effects you might feel

Most people notice mild issues that disappear on their own. The most frequent complaint is a sore or numb tongue, often called “peripheral neuropathy.” It feels like a tingling or burning sensation in your hands or feet. A simple vitamin B6 (pyridoxine) supplement usually clears it up, so doctors often prescribe it alongside isoniazid.

Other everyday side effects include nausea, loss of appetite, and fatigue. You might feel a bit dizzy when you stand up quickly— that's a temporary drop in blood pressure. Some folks get a mild rash or itching, which usually goes away without stopping the drug.

Signs that need a doctor’s attention

While most reactions are harmless, a few can be serious. The biggest red flag is liver trouble. Isoniazid can raise liver enzymes, leading to hepatitis. Watch for dark urine, yellow skin or eyes, unexplained stomach pain, or a fever that won’t break. If any of these pop up, call your doctor right away.

Another rare but concerning problem is severe allergic reaction. This can cause swelling of the face, lips, or throat, and trouble breathing. If you notice these signs, treat it as an emergency— call 911 or go to the nearest ER.

Sudden changes in mood, such as depression or anxiety, have also been linked to isoniazid in some cases. If you feel unusually low or have thoughts of self‑harm, reach out to a healthcare professional immediately.

To stay safe, keep a simple log of any new symptoms. Note when they started, how long they last, and if anything makes them better or worse. Bring this list to each check‑up; it helps your doctor decide whether you need a dose adjustment or extra tests.

Most people finish the full six‑month course without major issues. Taking the vitamin B6 supplement, staying hydrated, and reporting problems early are the best ways to protect yourself. Remember, stopping isoniazid on your own can let TB come back, so always discuss changes with your doctor first.