Isoniazid,
does it really help with Prevention of active tuberculosis in people with latent tuberculosis infection?
research showsIsoniazid is rated A because multiple placebo-controlled randomized trials synthesized in meta-analysis show prevention of active tuberculosis in people with latent or high-risk inactive infection. A Cochrane review of 11 trials and 73,375 participants found that at least six months of isoniazid reduced active tuberculosis to an RR of 0.40. Benefit was reproduced with both six- and twelve-month regimens across varied at-risk populations.
ads claimIt is incorrect to claim complete protection or treatment without testing. Active tuberculosis must first be excluded, and infection risk, reactivation risk, interactions, and hepatotoxicity must be assessed before preventive therapy.
Useful facts when choosing a product
- Isoniazid is an oral prescription preventive treatment for latent tuberculosis after active disease has been excluded, and recommended duration can vary by patient and local guidance.
- It can cause asymptomatic enzyme elevation or severe hepatitis, so alcohol use, underlying liver disease, interacting drugs, hepatitis symptoms, and liver tests when indicated require attention.
- Pyridoxine supplementation is considered for people at risk of peripheral neuropathy, including pregnancy, malnutrition, diabetes, or alcohol-use disorder, and adherence is important for preventive benefit.
What the research actually shows
The Cochrane review by Smieja and colleagues included 11 randomized trials and 73,375 at-risk people without active tuberculosis or known HIV infection, comparing at least six months of isoniazid with placebo. The RR for active tuberculosis was 0.40 (95% CI 0.31 to 0.52); six months had RR 0.44 and twelve months RR 0.38. Tuberculosis deaths fell but all-cause mortality did not, and hepatotoxicity was reported in 0.36% with six months and 0.52% with twelve months.
Why this is classified as A (92)
A meta-analysis of 11 placebo-controlled trials involving about 73,000 participants consistently reduced the direct endpoint of active tuberculosis to RR 0.40, yielding A with 92 points. Hepatitis, neuropathy, and treatment duration are separate safety and implementation issues.
Counterpoint. Shorter rifamycin-based latent-tuberculosis regimens may be preferred in some settings, but this reflects adherence, toxicity, and interaction tradeoffs rather than weak placebo-controlled efficacy for isoniazid.
Rejudgment record. New verdict — Applied A because a meta-analysis of 11 placebo-controlled randomized trials involving about 73,000 participants reproduced prevention of the direct hard endpoint of active tuberculosis
Sub-claim grades by effect
This ingredient is marketed for several effects. A single overall grade blends strong and weak claims together, so each effect is graded separately here. The overall grade reflects the strongest disconfirming or core claim.
| Effect (sub-claim) | Grade | Basis |
|---|---|---|
| Prevention of active tuberculosis | A | This direct disease-incidence endpoint was reproduced across 11 placebo-controlled trials involving about 73,000 participants, with RR 0.40. |
| Prevention with a six-month isoniazid regimen | A | The six-month regimen was also effective in meta-analysis, with RR 0.44. |
| Prevention with a twelve-month isoniazid regimen | A | The twelve-month regimen was effective in meta-analysis, with RR 0.38. |
Cross-check — Codex and Claude
Evidence Table
| Study | Design | Sample | Funding | Endpoint | Result | Weight |
|---|---|---|---|---|---|---|
| Smieja MJ et al. 2000 Cochrane review | Systematic review and meta-analysis of placebo-controlled randomized trials | 73,375 | Academic Cochrane review; authors reported no direct financial interest | Active tuberculosis over at least two years, tuberculosis death, all-cause death, and hepatotoxicity | Active tuberculosis RR was 0.40 (95% CI 0.31 to 0.52); both six and twelve months were effective. | Pivotal large synthesis of multiple randomized trials |
| International Union Against Tuberculosis Committee on Prophylaxis 1982 | International multicenter randomized preventive-therapy trial | 27,830 | International Union Against Tuberculosis multicenter study | Active tuberculosis over five years and hepatitis | Isoniazid preventive therapy reduced active tuberculosis and demonstrated effects related to duration and adherence. | Representative long-term direct disease-incidence trial |
Receipt — 2 References
All 2 cited sources were verified for existence at the original page (as of 2026-07-23).
Reviewed and approved: Chamgap Editorial Team · Approval date: 2026-07-23 · Corrections: none
Cite this verdict
[Chamgap] Isoniazid x prevention of active tuberculosis in latent infection — Evidence Grade A·92. 2 cited sources checked. Source: https://chamgap.com/en/verdicts/immunity/isoniazid-prevention-of-active-tuberculosis-in-latent-infection/ · CC BY 4.0CC BY 4.0 — free to use with attribution; do not distort grades, numbers, or verdict meaning.
What this document does and does not do
Chamgap is an information source. It reports what research has and has not confirmed; it does not tell readers what to take or buy. That decision belongs to readers and, when needed, medical or legal professionals. This verdict reflects literature available up to the search date and may change as new research appears. Nothing here is medical advice.