The short answer
High-dose nicotinic acid can worsen glucose control during repaglinide treatment. Review the niacin form and dose rather than assuming a time gap solves the problem.
What this answer covers
Niacin: pharmacologic nicotinic acid distinguished from nutritional amounts, nicotinamide and combination lipid medicines.
- Supplement or preparation
- Niacin
- Medication ingredient
- repaglinide
The issue is glucose control
The repaglinide label includes niacin among agents that may decrease its blood-glucose-lowering effect. High-dose nicotinic acid can increase insulin resistance and glucose production; this is not evidence that it blocks repaglinide absorption.
Which niacin exposure matters
Large therapeutic doses of nicotinic acid differ from ordinary nutrient intake and from other vitamin B3 forms. Bring the exact formulation and dose to the prescriber. A nutritional label reading niacin alone is not enough to determine risk.
Read the clinical study in context
A large trial of extended-release niacin combined with laropiprant found more serious disturbances in diabetes control. The combination and study population do not give a repaglinide-specific event rate.
Keep the prescribed medicine plan
Take repaglinide within thirty minutes before meals as prescribed and skip its dose when a meal is skipped. Review supplement changes with the prescriber instead of inventing a separation interval or adjusting the medicine yourself.
Watch for low blood sugar
Follow your existing glucose-monitoring and low-blood-sugar treatment plan. New sweating, shakiness, hunger or confusion warrants a glucose check when possible. Severe confusion, a seizure or inability to swallow safely needs emergency help.
Evidence and practical considerations
Absorption & effectiveness
Repaglinide labeling names niacin among medicines that may decrease glucose lowering; high-dose nicotinic acid evidence supports a conditional effectiveness concern, not reduced intestinal repaglinide absorption. A universal requirement to separate or avoid all vitamin B3 is unsupported.
- Exact scope
- Niacin: pharmacologic nicotinic acid distinguished from nutritional amounts, nicotinamide and combination lipid medicines. with Exact repaglinide oral tablets. Exact RxNorm IN73044 oral repaglinide; CYP2C8, CYP3A4 and transporters must not be equated with nateglinide pathways.
- Medication form and route
- oral
- Timing or duration
- Source-specific single-dose, repeated-dose and observational exposures distinguished.
What remains uncertain
- Large outcome trial used niacin plus laropiprant, not isolated niacin or a repaglinide subgroup. No validated spacing workaround, universal supplement cutoff or automatic dose change.
Factors that may matter: preparation and plant part; clinical indication; dose; other medicines; baseline alertness.
Read the supporting source summaries
Source 1: current product label
dailymed.nlm.nih.gov · Source check Sep 10, 2026
Population: People prescribed repaglinide.
Insulin secretagogue with hypoglycemia risk; within thirty minutes before meals and skip dose with skipped meal; nicotinic acid may reduce glucose-lowering effect, salicylates may increase it.
How this applies: Exact RxNorm IN73044 oral repaglinide; CYP2C8, CYP3A4 and transporters must not be equated with nateglinide pathways.
No universal supplement dose, interval, event rate or untested formulation equivalence.
Source 2: Federal nutrient guidance
ods.od.nih.gov · Source check Sep 10, 2026
Population: People taking antidiabetes medicines and high-dose nicotinic acid.
Large nicotinic-acid doses can raise glucose; monitoring is advised during co-use with antidiabetes medicines.
How this applies: Only the original species, preparation, population and measured endpoint apply. No exact-pair clinical rate inferred.
General guidance does not quantify repaglinide-specific risk or establish a timing workaround.
Source 3: Original human study
pubmed.ncbi.nlm.nih.gov · Source check Sep 10, 2026
Population: 25,673 patients with vascular disease.
Active treatment increased serious disturbances in diabetes control.
How this applies: Only the original species, preparation, population and measured endpoint apply. No exact-pair clinical rate inferred.
Combination treatment; does not isolate niacin from laropiprant or establish a repaglinide-specific rate.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Research summary published | |
| Article prepared | |
| Current exact available claims adjudicated using original captures and explicit identity and comparator limits. |
Article revision: 99482fcc1231ac35
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.