The short answer
Oral vitamin K1 can be used when recommended by your clinician. Long-term cholestyramine can lower vitamin K enough to cause a bleeding tendency; the label says this usually responds promptly to vitamin K1 by injection and that oral vitamin K1 can prevent it from recurring. Take oral vitamin K1 at least 1 hour before or 4 to 6 hours after cholestyramine, the label's spacing rule for other oral medicines. Serious deficiency is uncommon: clotting times stayed normal in 18 children treated for up to 2.5 years, but bleeding has been reported after 25 years of use, and in one 2025 case the deficiency persisted despite oral vitamin K while cholestyramine continued. Ask about a clotting test if you take cholestyramine long term, take warfarin, or have a bowel or liver condition.
What this answer covers
Vitamin K1 (phylloquinone, phytonadione) supplements taken with cholestyramine resin powder for oral suspension. Vitamin K2 products and prescription injectable vitamin K are outside this answer.
- Supplement or preparation
- vitamin K1
- Medication ingredient
- cholestyramine resin
What the label says
The cholestyramine label states that chronic use may be associated with an increased bleeding tendency due to low prothrombin from vitamin K deficiency, that this usually responds promptly to parenteral vitamin K1, and that recurrences can be prevented by oral vitamin K1. It lists prolonged prothrombin time and bruising among adverse reactions and says the resin may prevent absorption of fat-soluble vitamins. For other oral drugs it advises dosing at least 1 hour before or 4 to 6 hours after the resin.
What the case reports show
Bleeding from vitamin K deficiency has been reported after more than 25 years of cholestyramine in a patient with cholestatic liver disease, and the authors noted that earlier cases had appeared within weeks to months. In a 2025 report, a 57-year-old woman had profound vitamin K deficiency that did not correct with oral vitamin K while cholestyramine continued; the report does not say what form or timing of vitamin K was used.
Most people do not develop deficiency
In 18 children treated for up to 2.5 years, prothrombin time stayed normal throughout, and the authors recommended periodic testing rather than routine fat-soluble vitamins. Federal nutrient guidance says clinically significant vitamin K deficiency in adults is very rare, usually limited to malabsorption or interfering drugs, and calls the clinical significance of the sequestrant effect unclear while advising that vitamin K status be monitored, especially after many years.
Timing and form
Cholestyramine can interfere with absorption of oral vitamin K1. Follow the label's general spacing rule for other oral medicines: vitamin K1 at least 1 hour before or 4 to 6 hours after cholestyramine. The label describes injectable vitamin K1 as treatment for vitamin K deficiency-related bleeding tendency and oral vitamin K1 to prevent recurrence. An abnormal clotting test requires assessment of its cause and treatment by a clinician; it does not automatically establish vitamin K deficiency or a need for an injection. The 2025 case also shows that oral supplementation may fail during continued cholestyramine use.
Who should be monitored
A prothrombin time or INR check is reasonable for anyone on cholestyramine for years, and important for people on warfarin, people with liver disease, cholestasis, Crohn disease, short bowel or other malabsorption, and in pregnancy. Report easy bruising, nosebleeds, bleeding gums, blood in urine or stool, or unusually heavy periods promptly. If you take warfarin, do not start, stop or change vitamin K1 supplements without guidance from the clinician managing your anticoagulation, because changes in vitamin K intake can alter its effect.
Evidence and practical considerations
Side effects & toxicity
Chronic cholestyramine can cause vitamin K deficiency with a bleeding tendency that responds to vitamin K1; serious cases are rare, appear mainly with long use or liver and bowel disease, and one case was refractory to oral vitamin K while the resin continued.
- Exact scope
- Vitamin K1 (phylloquinone) supplements. with Cholestyramine resin powder for oral suspension (generic products, Questran and Prevalite) at any dose; the interaction happens in the gut because the resin is not absorbed.
- Medication form and route
- oral medication; oral supplement
What remains uncertain
- Label statement plus two case reports and one small pediatric series; no trial of oral vitamin K1 dosing or timing; the refractory case does not state the vitamin K form used.
Factors that may matter: Duration of cholestyramine use; Liver disease, cholestasis or bowel malabsorption; Warfarin or other anticoagulants; Dietary vitamin K intake.
Read the supporting source summaries
Source 1: current product label
dailymed.nlm.nih.gov · Source check Sep 22, 2026
Population: People prescribed cholestyramine resin
Chronic use may be associated with increased bleeding tendency due to hypoprothrombinemia from vitamin K deficiency; this usually responds promptly to parenteral vitamin K1, and recurrences can be prevented by oral administration of vitamin K1. Prolonged prothrombin time, ecchymosis and bleeding tendencies are listed among adverse reactions, and the resin may prevent absorption of fat-soluble vitamins including K. The label tells patients to take other drugs at least 1 hour before or 4 to 6 hours after cholestyramine, or at as great an interval as possible; it gives no vitamin-specific interval.
How this applies: Exact cholestyramine resin (RxCUI 2447) as oral powder for suspension; the innovator Questran label captured in this batch carries the same folate, vitamin K, fat-soluble vitamin and spacing wording.
The label gives no oral vitamin K1 dose, no monitoring schedule and no vitamin-specific interval.
Source 2: case report
pubmed.ncbi.nlm.nih.gov · Source check Sep 22, 2026
Population: One adult with intrahepatic cholestasis.
Haemorrhage from vitamin K deficiency occurred after over 25 years of use; the authors note only a few such cases had been reported, previously within weeks to months of starting, and call for awareness of fat-soluble vitamin depletion with long-term use.
How this applies: Shows that clinically serious vitamin K deficiency can appear very late and in liver disease; not a rate.
Single case in a patient with cholestatic liver disease, which itself impairs vitamin K absorption; abstract only.
Source 3: case report
pubmed.ncbi.nlm.nih.gov · Source check Sep 22, 2026
Population: One 57-year-old woman.
A 57-year-old woman developed profound vitamin K deficiency that was refractory to oral vitamin K while cholestyramine continued; the authors describe fat-soluble vitamin malabsorption as rarely clinically significant but capable of causing coagulopathy.
How this applies: Direct co-use report: oral vitamin K did not correct deficiency during continued cholestyramine, which argues for clotting tests rather than assuming a supplement is enough.
Abstract only; the vitamin K formulation, dose and timing relative to cholestyramine are not stated, so it cannot show whether separated oral vitamin K1 would have worked.
Source 4: original human study
pubmed.ncbi.nlm.nih.gov · Source check Sep 22, 2026
Population: Eighteen children with familial hypercholesterolaemia.
Prothrombin time remained normal in all patients; the authors advised measuring prothrombin time and vitamins A and E at intervals rather than routine fat-soluble vitamin supplementation.
How this applies: Shows that most people on prolonged cholestyramine do not develop a clotting abnormality.
Eighteen children, uncontrolled, abstract only; prothrombin time is an insensitive marker of vitamin K status.
Source 5: federal nutrient fact sheet
ods.od.nih.gov · Source check Sep 22, 2026
Population: General population; no cholestyramine co-use data
Vitamin K1 is phylloquinone. Bile acid sequestrants such as cholestyramine can reduce absorption of vitamin K and other fat-soluble vitamins, although the clinical significance is not clear, and vitamin K status should be monitored in people taking these drugs, especially for many years. Clinically significant deficiency in adults is very rare and usually limited to malabsorption disorders or drugs that interfere with vitamin K; bleeding is the classic sign, and people with malabsorption may need monitoring and sometimes supplementation.
How this applies: Names cholestyramine directly, supports monitoring rather than routine dosing, and identifies the higher-risk groups.
Consumer-level summary citing the same long-term case; no dose or interval.
Research assessment: · Open full citations ↗
Timing & monitoring
Take oral vitamin K1 at least 1 hour before or 4 to 6 hours after cholestyramine, following the label's rule for other oral drugs, and rely on clotting tests rather than assuming a supplement is sufficient during long-term use.
- Exact scope
- Oral vitamin K1 supplements at any dose. with Cholestyramine resin powder for oral suspension (generic products, Questran and Prevalite) at any dose; the interaction happens in the gut because the resin is not absorbed.
- Medication form and route
- oral medication; oral supplement
What remains uncertain
- No vitamin K1-specific interval has been tested; the label rule is written for other drugs.
Factors that may matter: Time between doses; Vitamin K1 dose and form; Warfarin or other anticoagulants.
Read the supporting source summaries
Source 1: current product label
dailymed.nlm.nih.gov · Source check Sep 22, 2026
Population: People prescribed cholestyramine resin
Chronic use may be associated with increased bleeding tendency due to hypoprothrombinemia from vitamin K deficiency; this usually responds promptly to parenteral vitamin K1, and recurrences can be prevented by oral administration of vitamin K1. Prolonged prothrombin time, ecchymosis and bleeding tendencies are listed among adverse reactions, and the resin may prevent absorption of fat-soluble vitamins including K. The label tells patients to take other drugs at least 1 hour before or 4 to 6 hours after cholestyramine, or at as great an interval as possible; it gives no vitamin-specific interval.
How this applies: Exact cholestyramine resin (RxCUI 2447) as oral powder for suspension; the innovator Questran label captured in this batch carries the same folate, vitamin K, fat-soluble vitamin and spacing wording.
The label gives no oral vitamin K1 dose, no monitoring schedule and no vitamin-specific interval.
Source 2: case report
pubmed.ncbi.nlm.nih.gov · Source check Sep 22, 2026
Population: One 57-year-old woman.
A 57-year-old woman developed profound vitamin K deficiency that was refractory to oral vitamin K while cholestyramine continued; the authors describe fat-soluble vitamin malabsorption as rarely clinically significant but capable of causing coagulopathy.
How this applies: Direct co-use report: oral vitamin K did not correct deficiency during continued cholestyramine, which argues for clotting tests rather than assuming a supplement is enough.
Abstract only; the vitamin K formulation, dose and timing relative to cholestyramine are not stated, so it cannot show whether separated oral vitamin K1 would have worked.
Source 3: federal nutrient fact sheet
ods.od.nih.gov · Source check Sep 22, 2026
Population: General population; no cholestyramine co-use data
Vitamin K1 is phylloquinone. Bile acid sequestrants such as cholestyramine can reduce absorption of vitamin K and other fat-soluble vitamins, although the clinical significance is not clear, and vitamin K status should be monitored in people taking these drugs, especially for many years. Clinically significant deficiency in adults is very rare and usually limited to malabsorption disorders or drugs that interfere with vitamin K; bleeding is the classic sign, and people with malabsorption may need monitoring and sometimes supplementation.
How this applies: Names cholestyramine directly, supports monitoring rather than routine dosing, and identifies the higher-risk groups.
Consumer-level summary citing the same long-term case; no dose or interval.
Research assessment: · Open full citations ↗
Review and change history
- Publication status
- Published research summary
- Clinical review
- Not yet recorded
| Date | Update |
|---|---|
| Editorial update | |
| Source-checked release edit clarified study design, exact evidence scope and practical wording. This research edit does not constitute clinical approval. | |
| Research summary published | |
| Article prepared | |
| Prepared exact cholestyramine resin and Vitamin K1 article from inspected current labeling and original sources, with uncertainty stated. |
Article revision: 1a3303bc269390c6
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.
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