The short answer
Aluminum-containing antacids may affect isoniazid absorption, but human results differ by preparation. The older study’s timing advice was isoniazid at least one hour before the antacid, not the antacid one hour before isoniazid.
What this answer covers
Oral aluminum-containing antacids, especially aluminum hydroxide gel; elemental aluminum and other routes are not equivalent.
- Supplement or preparation
- Aluminum
- Medication ingredient
- isoniazid
The older study found reduced and delayed uptake
The original1974 publisher abstract reports depressed and delayed isoniazid absorption with aluminum hydroxide gel; magaldrate effects were less pronounced and variable. Its recommendation placed the antibiotic before the antacid.
Later controlled studies found no significant change
A14-person aluminum-magnesium-antacid study and a12-person didanosine-placebo-buffer study found no significant effect on isoniazid exposure. These different formulations prevent treating reduced absorption as inevitable.
Keep the direction of any schedule explicit
The historical one-hour recommendation means isoniazid first and antacid later. It does not support giving aluminum antacid one hour before isoniazid, or prove that an unspecified two-hour reverse gap works. Ask the pharmacist for a schedule matched to the actual product.
Do not confuse food and antacid rules
Food can affect isoniazid exposure independently. Follow the prescribed medication instructions, identify the antacid ingredients and avoid changing the antibiotic dose to compensate for an assumed interaction.
Evidence and practical considerations
Timing & monitoring
Original Spanish-direction timing statement is not supported as written. Historical recommendation is isoniazid at least1 hour BEFORE antacid, not antacid1 hour before isoniazid; no validated generic reverse2 hour rule. Separate narrower timing finding retained.
- Exact scope
- Oral aluminum-containing antacids, especially aluminum hydroxide gel; elemental aluminum and other routes are not equivalent. with Isoniazid oral tablets.
- Medication form and route
- oral medication; oral supplement
What remains uncertain
- No unmeasured pair incidence, blanket class transfer or arbitrary spacing interval.
Factors that may matter: Preparation; Dose; Other medicines; Organ function.
Read the supporting source summaries
Source 1: current product label
dailymed.nlm.nih.gov · Source check Sep 11, 2026
Population: People prescribed isoniazid
Hepatitis and peripheral-neuropathy warnings; pyridoxine recommended in predisposed patients; tyramine/histamine food precautions.
How this applies: Exact isoniazid RxCUI 6038 IN, with stated salt/formulation/route bridge.
Exact route and formulation apply. Label precautions do not quantify untested botanical pairs or support arbitrary supplement doses.
Source 2: Original human study
academic.oup.com · Source check Sep 11, 2026
Population: Rat and human experiments.
Aluminum hydroxide delayed/depressed absorption; magaldrate effects smaller and variable. Authors recommended antibiotic at least1 hour before antacid.
How this applies: Original publisher abstract accessed, not complete article; no precise human dose/sample imported. Later studies found null results with other formulations.
Original publisher abstract accessed, not complete article; no precise human dose/sample imported. Later studies found null results with other formulations.
Source 3: Original human study
pubmed.ncbi.nlm.nih.gov · Source check Sep 11, 2026
Population: 14 healthy volunteers.
Antacid did not significantly change peak, time to peak or total exposure.
How this applies: Single-dose healthy14-person trial; preparation-specific, not proof all antacids lack effect.
Single-dose healthy14-person trial; preparation-specific, not proof all antacids lack effect.
Source 4: Original human study
pubmed.ncbi.nlm.nih.gov · Source check Sep 11, 2026
Population: 12 healthy volunteers.
No significant plasma pharmacokinetic effect.
How this applies: 12 healthy volunteers; placebo-buffer formulation, not all aluminum antacids. Full-body API/page unavailable.
12 healthy volunteers; placebo-buffer formulation, not all aluminum antacids. Full-body API/page unavailable.
Research assessment: · Open full citations ↗
Absorption & effectiveness
Preparation-dependent concern supported by1974 aluminum-hydroxide result, narrowed to oral antacids. Later14-person and12-person nulls retained; no all-aluminum or inevitable efficacy loss.
- Exact scope
- Oral aluminum-containing antacids, especially aluminum hydroxide gel; elemental aluminum and other routes are not equivalent. with Isoniazid oral tablets.
- Medication form and route
- oral medication; oral supplement
What remains uncertain
- No unmeasured pair incidence, blanket class transfer or arbitrary spacing interval.
Factors that may matter: Preparation; Dose; Other medicines; Organ function.
Read the supporting source summaries
Source 1: current product label
dailymed.nlm.nih.gov · Source check Sep 11, 2026
Population: People prescribed isoniazid
Hepatitis and peripheral-neuropathy warnings; pyridoxine recommended in predisposed patients; tyramine/histamine food precautions.
How this applies: Exact isoniazid RxCUI 6038 IN, with stated salt/formulation/route bridge.
Exact route and formulation apply. Label precautions do not quantify untested botanical pairs or support arbitrary supplement doses.
Source 2: Original human study
academic.oup.com · Source check Sep 11, 2026
Population: Rat and human experiments.
Aluminum hydroxide delayed/depressed absorption; magaldrate effects smaller and variable. Authors recommended antibiotic at least1 hour before antacid.
How this applies: Original publisher abstract accessed, not complete article; no precise human dose/sample imported. Later studies found null results with other formulations.
Original publisher abstract accessed, not complete article; no precise human dose/sample imported. Later studies found null results with other formulations.
Source 3: Original human study
pubmed.ncbi.nlm.nih.gov · Source check Sep 11, 2026
Population: 14 healthy volunteers.
Antacid did not significantly change peak, time to peak or total exposure.
How this applies: Single-dose healthy14-person trial; preparation-specific, not proof all antacids lack effect.
Single-dose healthy14-person trial; preparation-specific, not proof all antacids lack effect.
Source 4: Original human study
pubmed.ncbi.nlm.nih.gov · Source check Sep 11, 2026
Population: 12 healthy volunteers.
No significant plasma pharmacokinetic effect.
How this applies: 12 healthy volunteers; placebo-buffer formulation, not all aluminum antacids. Full-body API/page unavailable.
12 healthy volunteers; placebo-buffer formulation, not all aluminum antacids. Full-body API/page unavailable.
Research assessment: · Open full citations ↗
Timing & monitoring
For the historical aluminum-antacid precaution, the studied recommendation places isoniazid at least one hour before antacid; product-specific scheduling should be reviewed.
- Exact scope
- Oral aluminum-containing antacid. with Isoniazid oral tablets.
- Medication form and route
- oral medication; oral supplement
What remains uncertain
- No unmeasured exact-pair rate, all-preparation equivalence or arbitrary protective interval.
Factors that may matter: Preparation; Dose; Duration; Clinical risk factors.
Read the supporting source summaries
Source 1: Original human study
academic.oup.com · Source check Sep 11, 2026
Population: Rat and human experiments.
Aluminum hydroxide delayed/depressed absorption; magaldrate effects smaller and variable. Authors recommended antibiotic at least1 hour before antacid.
How this applies: Original publisher abstract accessed, not complete article; no precise human dose/sample imported. Later studies found null results with other formulations.
Original publisher abstract accessed, not complete article; no precise human dose/sample imported. Later studies found null results with other formulations.
Source 2: Original human study
pubmed.ncbi.nlm.nih.gov · Source check Sep 11, 2026
Population: 14 healthy volunteers.
Antacid did not significantly change peak, time to peak or total exposure.
How this applies: Single-dose healthy14-person trial; preparation-specific, not proof all antacids lack effect.
Single-dose healthy14-person trial; preparation-specific, not proof all antacids lack effect.
Source 3: Original human study
pubmed.ncbi.nlm.nih.gov · Source check Sep 11, 2026
Population: 12 healthy volunteers.
No significant plasma pharmacokinetic effect.
How this applies: 12 healthy volunteers; placebo-buffer formulation, not all aluminum antacids. Full-body API/page unavailable.
12 healthy volunteers; placebo-buffer formulation, not all aluminum antacids. Full-body API/page unavailable.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Research summary published | |
| Editorial update | |
| Corrected missing spaces between numbers and units or words in the copy before registration; evidence and conclusions unchanged. | |
| Article prepared | |
| Prepared exact isoniazid article with formulation-specific evidence and uncertainty. |
Article revision: 961de43d7a14da1a
This guide brings together the evidence records used by our interaction checker. Each finding retains its own preparation limits, research date, and source summaries.
Full citations require verification. Reading this answer and the source summaries does not.
Taking other supplements or medications?
Use the checker to explore your other combinations. Ask a pharmacist to review the exact products, amounts and medical conditions in your complete list.
Open the interaction checkerInformation, not medical advice. Do not change prescribed treatment based on this guide.