Vitamin D3 and medications.
Vitamin D3 is classified as a foundation supplement in the Distil database, evidence Grade A. The page below lists every medication we have explicitly assessed it against.
Vitamin D3 is the form your skin makes from sunlight, and at UK latitudes there is not enough sun between October and April to make it, which is why deficiency is so common, especially in people with darker skin, indoor workers, and anyone over 50. It supports bone density, immune function, mood, and calcium regulation, and the evidence here is strong: a 25-trial meta-analysis found supplementation reduced respiratory infections. Testing beats guessing the dose: the UK sufficiency threshold is a blood level of 50 nmol/L, below 25 nmol/L counts as deficient, and higher targets sold as optimal are debated rather than established. Two interactions matter most. Magnesium is needed to convert D3 into its active form, so the two tend to work best taken together. Vitamin K2 helps direct calcium to bone rather than arteries, which is why D3 is rarely recommended alone. Thiazide diuretics raise calcium and warrant a word with your GP. Take it with food, and retest after a few months rather than dosing blind.
Below are the 10 documented pairs we have explicitly assessed for Vitamin D3: 6 amber and 4 green. The pairs cluster around 4 mechanisms: Absorption interference, Drug depletes the supplement, Hypercalcaemia risk, and Beneficial combination. Every call is cited to either a clinical reference (PMID) or the British National Formulary. Anything not listed here is either still to be assessed or beyond our database scope. The checker beneath surfaces assessments by medication, and the missing-item form at the bottom of the page routes any uncatalogued medication into our next curation pass.
Documented interactions
Last reviewed 10 June 2026. Each interaction below lists the evidence its assessment drew on: some rest on studies of the exact pair, others on mechanism evidence, where a citation may support one part of the reasoning rather than the exact combination. The evidence line on each entry says which.
Absorption interference
Amber Does interact with Orlistat?
Orlistat works by blocking the gut from absorbing some dietary fat, and because vitamin D is fat-soluble it gets absorbed less well too. This may lower your vitamin D level over time, even if you take a supplement at the same time of day. The usual advice is to separate them: take your vitamin D (or a fat-soluble multivitamin) at bedtime, at least 2 hours away from any orlistat dose, and your prescriber may check your vitamin D level.
Evidence: Supported by human study data.
Drug depletes the supplement
Amber Does interact with Carbamazepine?
Carbamazepine speeds up the liver enzymes that break vitamin D down, so people on it for a long time tend to have lower vitamin D levels and, over years, a higher risk of weaker bones. This works the opposite way to most interactions: the medicine lowers your vitamin D rather than the supplement affecting the medicine. Taking a vitamin D supplement is generally the recommended response, and many prescribers check vitamin D and bone health in people on long-term carbamazepine.
Evidence: Supported by human study data.
Amber Does interact with Phenytoin?
Phenytoin speeds up the breakdown of vitamin D in the body, so people on long-term phenytoin often have lower vitamin D levels and, over years, can lose bone density. This is a reason to take vitamin D rather than avoid it: many specialists check vitamin D and supplement people on long-term phenytoin. It is worth letting your prescriber know so your vitamin D level and bone health can be kept under review and the dose set for you.
Evidence: Supported by human study data.
Hypercalcaemia risk
Amber Does interact with Bendroflumethiazide?
Thiazide diuretics like bendroflumethiazide make the kidneys hold on to more calcium, and vitamin D raises how much calcium you absorb from food. Taken together, especially at higher vitamin D doses or alongside calcium supplements, the two may push blood calcium too high. It is worth your prescriber knowing you take both; standard replacement doses of vitamin D tend to be fine when your blood calcium is checked routinely.
Evidence: Supported by human study data.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Amber Does interact with Digoxin?
High-dose vitamin D can raise blood calcium, and a high calcium level makes the heart more sensitive to digoxin, which already has a narrow safe range. Standard replacement doses of vitamin D with normal calcium are not expected to be a problem, but high-dose vitamin D, or vitamin D plus calcium supplements, is worth discussing with your prescriber so your calcium and digoxin can be kept in check.
Evidence: Supported by human study data.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Amber Does interact with Indapamide?
Indapamide is a thiazide-like diuretic that makes the kidneys keep more calcium, and vitamin D increases how much calcium you absorb. Together, particularly at higher vitamin D doses or with calcium supplements, blood calcium may rise too high. Let your prescriber know you take both; normal replacement doses of vitamin D are usually fine when your blood calcium is checked from time to time.
Evidence: Supported by human study data.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Beneficial combination
Green Does interact with Alendronic acid?
Vitamin D and alendronic acid are expected to be taken together. Adequate vitamin D is recommended alongside a bisphosphonate like alendronic acid: it helps keep your blood calcium in a healthy range and supports the medicine working as intended. The one practical point is timing, not safety. Alendronic acid must be taken first thing on an empty stomach with plain water, staying upright for 30 minutes, so take any vitamin D product (especially a combined vitamin D plus calcium supplement) later in the day. If your vitamin D is very low, your GP may want to correct it before or as you start, so ask them to confirm your levels.
Evidence: Supported by human study data.
Green Does interact with Methylprednisolone acetate?
Vitamin D and methylprednisolone are usually a helpful pairing rather than a problem when the methylprednisolone is taken by mouth or injection for three months or more. Long-term steroids weaken bone and reduce how well you absorb calcium, so vitamin D (often with calcium) is routinely recommended alongside them to protect your bones. Short courses and one-off injections do not carry the same concern. At very high steroid doses the bone-protecting effect of vitamin D may be partly blunted, so if you are on long-term or high-dose steroids your prescriber may also check your bone health and consider additional bone medication.
Evidence: Supported by human study data.
Green Does interact with Prednisolone?
Vitamin D and prednisolone are usually a helpful pairing rather than a problem. Long-term steroids like prednisolone weaken bone and reduce how well you absorb calcium, so vitamin D (often with calcium) is routinely recommended alongside them to protect your bones. Guidelines advise keeping vitamin D in a healthy range for anyone taking steroids for three months or more. At very high steroid doses the bone-protecting effect of vitamin D may be partly blunted, so if you are on long-term or high-dose steroids your prescriber may also check your bone health and consider additional bone medication.
Evidence: Supported by human study data.
Green Does interact with Risedronate sodium?
Vitamin D and risedronate are commonly and deliberately taken together. Risedronate works best when your vitamin D level is in a healthy range, and keeping vitamin D topped up lowers the small chance of your blood calcium dropping after a dose. This is a helpful pairing, not a clash. Take risedronate first thing on an empty stomach with plain water and stay upright for 30 minutes; you can take your vitamin D later in the day.
Evidence: Supported by human study data.
What this list does not say. Pairs not flagged here are not implicitly safe. They are either not yet in our database, or fall outside our inclusion scope. Use the checker below to surface any medication, and submit a missing item if you take something we have not catalogued.
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How we grade severity, choose what's in scope, and what we exclude.
Every call on this page is reasoned. We publish the full rubric for severity tiers, the medication inclusion logic, the evidence grades we accept, and what we deliberately leave out. About three thousand words. Worth reading once if you use this tool more than occasionally.
Read the full methodologyA full supplement review, built around you, not a generic stack.
The free checker answers one interaction question at a time. A Distil report reviews the bigger picture: your goals, diet, medications, current supplements and any blood results you provide, then shows what appears worth keeping, changing, adding or leaving out.
- what your diet already covers, so you are not adding a capsule for something food is already handling
- which evidence-graded compounds are worth considering for your goals, and which were considered but left out
- what to keep, change or stop from what you already take, plus the order to introduce anything new
- how your medications and complete supplement stack fit together, with daily timing and a clear point for reassessment
The interaction check is one section of the full report. You also get the reasoning behind each recommendation and the evidence references used.
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