The short answer
Pharmacologic niacin can weaken insulin isophane’s glucose-lowering effect and worsen glucose control. This is different from claiming that ordinary food-level vitamin B3 causes the same risk.
What this answer covers
Oral niacin, especially pharmacologic nicotinic acid; dietary vitamin B3 and nicotinamide are different exposures.
- Supplement or preparation
- Niacin
- Medication ingredient
- insulin isophane
The NPH labels name niacin
Humulin N and Novolin N list niacin among agents that may reduce glucose lowering. Increased monitoring and clinician-directed treatment review may be needed.
Clinical evidence concerns a high-dose combination
A large vascular-risk trial of extended-release niacin plus laropiprant found more serious disturbances in diabetes control. It was not an glulisine-specific comparison, and laropiprant prevents attributing every outcome to niacin alone.
Dose and form matter
The trial concerned high-dose extended-release nicotinic acid with laropiprant. Its findings do not demonstrate the same risk from ordinary dietary vitamin B3 or every nicotinamide product.
Plan starting and stopping
Discuss pharmacologic niacin changes with the diabetes team and review glucose readings. A short spacing interval is not established to prevent this systemic effect. Do not change insulin independently.
Evidence and practical considerations
Side effects & toxicity
Exact human NPH labels name niacin as potentially reducing glucose lowering; narrowed to pharmacologic exposure and monitoring.
- Exact scope
- Oral niacin, especially pharmacologic nicotinic acid; dietary vitamin B3 and nicotinamide are different exposures. with Insulin isophane RxCUI1605101 IN; human NPH subcutaneous suspension label bridge.
- Medication form and route
- subcutaneous insulin isophane; oral supplement
What remains uncertain
- No exact event rate or arbitrary dose adjustment.
Factors that may matter: Product; Dose; Meals; Other diabetes treatment.
Read the supporting source summaries
Source 1: current product label
dailymed.nlm.nih.gov · Source check Sep 10, 2026
Population: Patients prescribed human NPH insulin
Hypoglycemia can be severe. Niacin may reduce glucose lowering. Changes in glucose-active treatments and meals can require monitoring and clinician review. Intravenous and pump use prohibited.
How this applies: RxCUI1605101 IN insulin isophane; human NPH formulation bridge explicit.
Human NPH labels inform the generic insulin-isophane ingredient. Not animal insulin, rapid analogs or automatically every premix. No herb-specific event rate.
Source 2: current product label
dailymed.nlm.nih.gov · Source check Sep 10, 2026
Population: Patients prescribed human NPH insulin
Hypoglycemia can be severe. Niacin may reduce glucose lowering. Changes in glucose-active treatments and meals can require monitoring and clinician review. Intravenous and pump use prohibited.
How this applies: RxCUI1605101 IN insulin isophane; human NPH formulation bridge explicit.
Human NPH labels inform the generic insulin-isophane ingredient. Not animal insulin, rapid analogs or automatically every premix. No herb-specific event rate.
Source 3: original human study
pubmed.ncbi.nlm.nih.gov · Source check Sep 10, 2026
Population: 25,673high-vascular-risk adults.
High-dose niacin-laropiprant increased serious disturbances in diabetes control compared with placebo.
How this applies: Indirect for exact insulin isophane; study drug, supplement form and outcome retained.
Combination product, not ordinary nutritional niacin or a glipizide-specific estimate; no supplement need or protective spacing demonstrated. This does not establish an exact insulin-isophane interaction.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Article prepared | |
| Prepared exact isophane article with human NPH product bridge and source-specific clinical limits. | |
| Research summary published |
Article revision: 5ad0aab023ad88a5
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.