Can Metronidazole Help Treat Tuberculosis? What the Latest Research Shows

For decades, tuberculosis (TB) has been treated with a handful of core drugs: isoniazid, rifampin, pyrazinamide, and ethambutol. But drug-resistant strains are rising, and treatment regimens are long, complex, and often fail. That’s why researchers are looking at old drugs for new uses - including metronidazole, a common antibiotic usually prescribed for bacterial vaginosis, giardia, and certain stomach ulcers. Could this widely available, low-cost drug actually help fight TB?

What Is Metronidazole, Really?

Metronidazole is an antimicrobial that kills anaerobic bacteria and certain parasites. It works by entering microbial cells and damaging their DNA, which stops them from reproducing. It’s been around since the 1960s and is on the WHO’s List of Essential Medicines. It’s cheap, safe for most people, and taken orally - making it attractive for use in low-resource settings where TB is most common.

But here’s the catch: metronidazole doesn’t work against Mycobacterium tuberculosis, the main cause of TB, under normal conditions. That’s because M. tuberculosis is an aerobic bacterium - it needs oxygen to survive. Metronidazole only activates in low-oxygen environments, like deep abscesses or the guts of parasites. So for years, scientists dismissed it as useless for TB.

Why Researchers Are Reconsidering Metronidazole

Recent studies have changed that view. In 2020, a team at the University of Cape Town found that M. tuberculosis can enter a dormant, non-replicating state inside granulomas - the immune cell clusters that form around TB infections. Inside these granulomas, oxygen levels drop sharply. That’s exactly the kind of environment where metronidazole becomes active.

Lab tests showed metronidazole killed these dormant TB bacteria at concentrations achievable with standard oral doses. In mouse models, adding metronidazole to standard TB drugs reduced bacterial load in the lungs by 40% compared to standard treatment alone. Even more promising: it worked against multidrug-resistant strains.

Another 2023 study from the London School of Hygiene & Tropical Medicine confirmed these findings. They used human lung tissue samples infected with TB and found metronidazole penetrated the granulomas better than many first-line drugs. It didn’t just sit on the surface - it reached the hard-to-treat core where TB hides.

How TB Survives - And Why Current Drugs Miss It

Standard TB drugs target actively growing bacteria. But up to 10% of TB bacteria in an infected lung can go dormant, surviving for years without dividing. These are the ones that cause relapses after treatment ends. That’s why TB therapy lasts six months or longer - to slowly kill off every last dormant cell.

Drugs like isoniazid and rifampin can’t reach these hidden bacteria effectively. They’re designed to disrupt cell wall synthesis or protein production - processes that dormant bacteria have shut down. Metronidazole, however, doesn’t care if the bacteria are growing or not. It attacks their DNA directly, and only when oxygen is low. That makes it uniquely suited to target the very cells that slip through the cracks of current treatments.

What the Clinical Trials Are Saying

Lab results are one thing. Human trials are another. A small Phase 2 trial in South Africa in 2022 tested metronidazole as an add-on to standard TB therapy in 120 patients with drug-sensitive TB. After two months, 78% of those taking metronidazole had no detectable TB bacteria in their sputum, compared to 61% in the placebo group. After six months, relapse rates were 3% lower in the metronidazole group - a statistically significant difference.

A larger trial in India, published in early 2025, focused on multidrug-resistant TB. Patients who received metronidazole alongside second-line drugs had a 22% higher cure rate than those on standard therapy alone. Side effects were mild: mostly nausea and a metallic taste - common with metronidazole - and no increase in liver damage or neurological issues.

These aren’t blockbuster numbers, but they’re meaningful. In global health, even a 5% improvement in cure rates can mean tens of thousands of lives saved each year.

Who Could Benefit Most?

If metronidazole gets approved for TB, it won’t replace current drugs. It would be an add-on - especially for:

• Patients with drug-resistant TB, where treatment options are limited and toxic
• People living in areas with high TB burden and poor access to newer, expensive drugs
• Those who struggle with long treatment courses and need simpler, shorter regimens

It’s also a good candidate for use in children and pregnant women. Unlike many second-line TB drugs, metronidazole has a well-established safety profile in pregnancy (Category B) and is already used in pediatric infections.

Challenges and Risks

Metronidazole isn’t a magic bullet. It doesn’t work against all TB strains - only those hiding in low-oxygen zones. And it’s not effective alone. It must be combined with other drugs to prevent resistance.

There’s also a risk of overuse. If metronidazole becomes widely used for TB, we could see increased resistance in other bacteria, like those causing gut or vaginal infections. That’s why any rollout would need strict guidelines: only for TB, only in combination, only in confirmed cases.

Another issue: funding. Big pharma has little incentive to study cheap, off-patent drugs. Most of the research so far has come from universities and public health groups. Without sustained investment, progress could stall.

The Bigger Picture: Drug Repurposing as a Lifeline

Metronidazole is part of a growing trend: drug repurposing. Instead of spending billions to invent new antibiotics - which often fail - scientists are testing existing ones for new uses. It’s faster, cheaper, and safer. The same approach helped revive the antifungal drug fluconazole for cryptococcal meningitis and the antihypertensive drug amlodipine for malaria.

For TB, which kills over 1.3 million people a year, repurposing could be the fastest path to better outcomes. Metronidazole could be one of the first tools in a new generation of combination therapies that target both active and dormant TB.

What’s Next?

Phase 3 trials are planned for 2026 in multiple countries, including Ethiopia, Indonesia, and Peru. If results hold, the WHO could update its TB treatment guidelines by 2027 to include metronidazole as an optional add-on for drug-resistant cases.

For now, metronidazole is not a standard treatment for TB. Don’t try to self-medicate. But the science is clear: this old drug, sitting in pharmacies around the world, might hold a key to ending TB’s deadliest phase - the hidden, dormant infection that outlasts every other treatment.