The short answer
Yes: take vitamin K1 at least 4 hours before colesevelam. The label tells anyone on oral vitamin supplements to take them at least 4 hours before colesevelam because it may reduce absorption of fat-soluble vitamins including vitamin K, and it names people on warfarin and people with malabsorption as those at higher risk of vitamin K deficiency. The interval is before, not after, the colesevelam dose. The studies reviewed did not establish a deficiency signal: clotting factors did not differ from placebo in the adolescent trial, and adult trial reviews report no clinically significant changes in vitamins or coagulation. If you take warfarin, the label calls for frequent INR checks when colesevelam is started.
What this answer covers
Vitamin K1 (phylloquinone, phytonadione) supplements taken with colesevelam hydrochloride tablets or oral suspension. Vitamin K2 products and injectable vitamin K are outside this answer.
- Supplement or preparation
- vitamin K1
- Medication ingredient
- colesevelam
What the label says
The WELCHOL label warns that colesevelam may decrease absorption of fat-soluble vitamins A, D, E and K, that people susceptible to vitamin K deficiency such as those on warfarin or with malabsorption syndromes may be at increased risk, and that patients on oral vitamin supplementation should take their vitamins at least 4 hours before colesevelam. For warfarin it reports postmarketing reduced INR and directs frequent INR monitoring during initiation, then periodically. It also reports no significant effects on fat-soluble vitamin levels or clotting factors relative to placebo in the adolescent study.
Why 4 hours before
Colesevelam is a non-absorbed polymer that binds bile acids and some other substances in the gut. In healthy volunteers, prescription drugs swallowed with colesevelam lost exposure, while taking them 4 hours before colesevelam removed the interaction. The label applies the same 4-hours-before window to oral vitamins and gives no interval for taking them after colesevelam. For example, vitamins with breakfast and colesevelam with a later meal can work if there is at least a 4-hour gap before every colesevelam dose and the timing fits your prescribed schedule.
How likely is vitamin K deficiency
The pediatric study enrolled 194 children aged 10 to 17. It compared colesevelam with placebo for 8 weeks, followed by an 18-week open-label phase in which all participants received colesevelam. The label reports no significant effects on fat-soluble vitamin levels or clotting factors relative to placebo; this was not a 26-week placebo comparison. A review of adult trials reported no clinically significant vitamin or coagulation changes. These short-term results do not establish the long-term risk of deficiency. Federal guidance for bile acid sequestrants names cholestyramine and colestipol, not colesevelam; it recommends monitoring vitamin K status, especially after many years.
Warfarin and other risk groups
If you take warfarin, the label's own instruction is frequent INR monitoring when colesevelam starts; vitamin K1 supplements change INR, so do not start or stop them without the anticoagulation clinic knowing. People with Crohn disease, celiac disease, short bowel, cystic fibrosis, bile duct disease or prior weight-loss surgery are the other group the label flags. Report easy bruising, nosebleeds, bleeding gums or blood in urine or stool.
Evidence and practical considerations
Timing & monitoring
Take oral vitamin K1 at least 4 hours before colesevelam, as the label directs for oral vitamin supplements, with INR monitoring for people on warfarin; the 4-hours-before window eliminated interactions for tested drugs, and no interval after colesevelam is labeled.
- Exact scope
- Oral vitamin K1 supplements at any dose. with Colesevelam hydrochloride tablets and powder for oral suspension (WELCHOL and generics), 3.75 g daily; the polymer is not absorbed, so any effect happens in the gut.
- Medication form and route
- oral medication; oral supplement
What remains uncertain
- The label instruction is class-wide for vitamins; the interval evidence comes from prescription drugs, not vitamin K1.
Factors that may matter: Time between doses; Warfarin or other anticoagulants; Underlying malabsorption.
Read the supporting source summaries
Source 1: current product label
dailymed.nlm.nih.gov · Source check Sep 22, 2026
Population: People prescribed colesevelam
WELCHOL may decrease absorption of fat-soluble vitamins A, D, E and K. Patients with a susceptibility to vitamin K deficiency, for example those on warfarin or with malabsorption syndromes, may be at increased risk. Patients on oral vitamin supplementation should take their vitamins at least 4 hours prior to WELCHOL. For warfarin the label reports postmarketing reduced INR and directs frequent INR monitoring at initiation then periodically. In the adolescent study there were no significant effects on fat-soluble vitamin levels or clotting factors relative to placebo.
How this applies: Exact colesevelam hydrochloride (RxCUI 141626) tablets and oral suspension; the vitamin instruction covers oral vitamin supplements as a group.
No vitamin K1 dose, no clotting-test schedule for people not on warfarin, and no after-dose interval are given.
Source 2: original human study
pubmed.ncbi.nlm.nih.gov · Source check Sep 22, 2026
Population: Healthy adult volunteers in six open-label randomized studies.
Concomitant colesevelam lowered exposure to glyburide, levothyroxine and ethinyl estradiol and the peak of repaglinide and norethindrone; when the drug was taken 4 hours before colesevelam no interaction was observed, and the authors concluded a 4-hour window appears sufficient.
How this applies: Explains the label's 4-hours-before rule and the direction (before, not after); it is not vitamin-specific.
Tested prescription drugs, not vitamins; single doses in healthy volunteers.
Source 3: clinical review
pmc.ncbi.nlm.nih.gov · Source check Sep 22, 2026
Population: Children and adolescents with heterozygous familial hypercholesterolemia.
Colesevelam may decrease absorption of some medications such as multivitamins and should be given at least four hours after them; absorption of fat-soluble vitamins may be decreased; the authors call for further trials on long-term complications such as fat-soluble vitamin depletion. They suggest giving colesevelam with dinner, or split between lunch and dinner, when vitamins are taken at breakfast.
How this applies: Full-text review confirming the label's timing direction and the absence of long-term vitamin data.
Review, not original data; its four-hour advice restates the label.
Source 4: federal nutrient fact sheet
ods.od.nih.gov · Source check Sep 22, 2026
Population: General population; no colesevelam co-use data
Vitamin K1 is phylloquinone. Bile acid sequestrants such as cholestyramine and colestipol 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 or interfering drugs; bleeding is the classic sign.
How this applies: Applies to colesevelam only as a member of the bile acid sequestrant class; supports monitoring rather than routine dosing and identifies the risk groups.
Names cholestyramine and colestipol, not colesevelam; class-level statement without a dose or interval.
Research assessment: · Open full citations ↗
Side effects & toxicity
Colesevelam is labeled as possibly decreasing vitamin K absorption with higher risk on warfarin or with malabsorption, but clotting factors and fat-soluble vitamin levels did not differ from placebo in the adolescent trial and adult reviews report no clinically significant coagulation changes.
- Exact scope
- Vitamin K1 supplements. with Colesevelam hydrochloride tablets and powder for oral suspension (WELCHOL and generics), 3.75 g daily; the polymer is not absorbed, so any effect happens in the gut.
- Medication form and route
- oral medication; oral supplement
What remains uncertain
- Coagulation results are read from the label and reviews rather than primary abstracts; 6 to 26 weeks; no data with supplements or in malabsorption; class guidance names other sequestrants.
Factors that may matter: Warfarin or other anticoagulants; Underlying malabsorption; Duration of colesevelam use.
Read the supporting source summaries
Source 1: current product label
dailymed.nlm.nih.gov · Source check Sep 22, 2026
Population: People prescribed colesevelam
WELCHOL may decrease absorption of fat-soluble vitamins A, D, E and K. Patients with a susceptibility to vitamin K deficiency, for example those on warfarin or with malabsorption syndromes, may be at increased risk. Patients on oral vitamin supplementation should take their vitamins at least 4 hours prior to WELCHOL. For warfarin the label reports postmarketing reduced INR and directs frequent INR monitoring at initiation then periodically. In the adolescent study there were no significant effects on fat-soluble vitamin levels or clotting factors relative to placebo.
How this applies: Exact colesevelam hydrochloride (RxCUI 141626) tablets and oral suspension; the vitamin instruction covers oral vitamin supplements as a group.
No vitamin K1 dose, no clotting-test schedule for people not on warfarin, and no after-dose interval are given.
Source 2: original human study
pubmed.ncbi.nlm.nih.gov · Source check Sep 22, 2026
Population: One hundred and ninety-four children aged 10 to 17 years, 129 treated with colesevelam.
LDL-cholesterol fell 12.5 percent with 3.75 g daily versus placebo; the abstract reports lipid results and that adverse events were evaluated, but gives no vitamin values. The WELCHOL label (section 8.4) draws on this population for its statement that fat-soluble vitamin levels and clotting factors showed no significant effects relative to placebo.
How this applies: The controlled study behind the label's null fat-soluble vitamin statement; adolescents without malabsorption.
Vitamin outcomes are not in the abstract; the null vitamin statement is read from the label, not the paper; 26 weeks total.
Source 3: review of clinical trials
pubmed.ncbi.nlm.nih.gov · Source check Sep 22, 2026
Population: Adults with primary hypercholesterolemia in the early trials.
In humans colesevelam did not induce clinically significant changes in serum levels of vitamins, coagulation parameters or liver enzymes; it did not alter the pharmacokinetics of several co-administered drugs.
How this applies: Summarizes the adult trial vitamin data that the primary abstracts omit; medication-only exposure.
Narrative review read as an abstract; underlying vitamin data are not shown; trials lasted 6 to 24 weeks.
Source 4: federal nutrient fact sheet
ods.od.nih.gov · Source check Sep 22, 2026
Population: General population; no colesevelam co-use data
Vitamin K1 is phylloquinone. Bile acid sequestrants such as cholestyramine and colestipol 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 or interfering drugs; bleeding is the classic sign.
How this applies: Applies to colesevelam only as a member of the bile acid sequestrant class; supports monitoring rather than routine dosing and identifies the risk groups.
Names cholestyramine and colestipol, not colesevelam; class-level statement without a 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 colesevelam and Vitamin K1 article from inspected current labeling and original sources, with uncertainty stated. |
Article revision: 03470457d3f96f47
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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