Isoniazid Drug Interactions: What You Need to Know Before Taking It

When you take isoniazid, a first-line antibiotic used to treat and prevent tuberculosis. Also known as INH, it’s one of the most effective drugs for killing TB bacteria—but it doesn’t play well with many other medications. This isn’t just a minor warning. Isoniazid can trigger dangerous reactions when mixed with common drugs like rifampin, a tuberculosis antibiotic often prescribed alongside isoniazid, or even over-the-counter pain relievers. The risk isn’t theoretical—it’s documented in real patients who ended up in the hospital because their liver couldn’t handle the combo.

Isoniazid affects how your liver breaks down other drugs. It can either slow down metabolism, causing buildup and toxicity, or speed it up, making other meds useless. For example, mixing isoniazid with alcohol, even small amounts raises your chance of severe liver damage. That’s why doctors tell you to skip beer, wine, or hard liquor while on this drug. It also interacts badly with selegiline, an antidepressant used for Parkinson’s, because both affect brain chemicals in similar ways. Together, they can cause a life-threatening spike in blood pressure or serotonin syndrome. And if you’re on warfarin, a blood thinner, isoniazid can make it too strong, increasing your risk of bleeding.

It’s not just prescription drugs. Even something as simple as vitamin B6, often taken to prevent nerve side effects from isoniazid, needs careful dosing. Too little and you risk tingling or numbness in your hands and feet; too much and you might mask early signs of toxicity. And don’t assume herbal supplements are safe—St. John’s wort, kava, and even high-dose niacin can make liver damage worse. The bottom line: if you’re taking isoniazid, your entire medication list needs a second look. Your doctor or pharmacist should review every pill, patch, and capsule you use—even those you’ve taken for years.

That’s why the posts below cover real-world cases, warning signs, and practical steps to avoid dangerous mix-ups. You’ll find clear breakdowns of what happens when isoniazid meets other drugs, how to spot early liver trouble, and how to talk to your provider about your full medication history. Whether you’re on TB treatment now or just starting, this collection gives you the facts you need to stay safe—not just informed.