Spirulina and medications.
Spirulina is in the Distil supplement database, evidence Grade B. The page below lists every medication we have explicitly assessed it against.
Spirulina is a blue-green algae taken as a dried powder or tablet, valued mainly for its antioxidant and metabolic effects. A dose-response meta-analysis of 20 trials found it tends to lower LDL cholesterol, total cholesterol and triglycerides while raising HDL, which is the basis of its Grade B rating, alongside smaller signals for blood pressure and blood glucose. Two honest limits are worth knowing. Its B12 content is an analogue your body cannot use, so it does not replace methylcobalamin. And sourcing matters: poorly sourced spirulina can carry microcystin contamination and heavy metals, so third-party purity certification is not optional. People on immunosuppressants or with autoimmune conditions should avoid it: spirulina is immunomodulating, and there are documented case reports of it precipitating autoimmune flares (Lee and Werth 2004). It is also contraindicated in phenylketonuria because of its phenylalanine content. Typical doses sit between 1 and 8g daily. Useful for broad metabolic support, particularly in vegans, provided the product is certified clean.
Below are the 12 documented pairs we have explicitly assessed for Spirulina: 12 amber. The pairs cluster around 3 mechanisms: Additive blood-pressure lowering, Additive anticoagulation, and Immune-stimulant vs immunosuppressant (precautionary). 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 14 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.
Additive blood-pressure lowering
Amber Does interact with Amlodipine?
Spirulina has a mild blood-pressure-lowering effect of its own, shown in human trials. Amlodipine lowers blood pressure through calcium-channel blockade. Used together, the combined effect tends to be a little larger than the medicine alone. Watch for dizziness on standing in the first couple of weeks, and tell your GP if it happens so your dose can be reviewed.
Evidence: Limited human data, based on case reports and a known mechanism.
Amber Does interact with Bisoprolol?
Spirulina has a mild blood-pressure-lowering effect of its own, shown in human trials. Bisoprolol lowers blood pressure mainly by slowing the heart and easing its workload. Used together, the combined effect tends to be a little larger than the medicine alone. Watch for dizziness on standing in the first couple of weeks, and tell your GP if it happens so your dose can be reviewed.
Evidence: Limited human data, based on case reports and a known mechanism.
Amber Does interact with Candesartan cilexetil?
Spirulina has a mild blood-pressure-lowering effect of its own, shown in human trials. Candesartan lowers blood pressure by blocking the angiotensin II receptor. Used together, the combined effect tends to be a little larger than the medicine alone. Watch for dizziness on standing in the first couple of weeks, and tell your GP if it happens so your dose can be reviewed.
Evidence: Limited human data, based on case reports and a known mechanism.
Amber Does interact with Diltiazem hydrochloride?
Spirulina has a mild blood-pressure-lowering effect of its own, shown in human trials. Diltiazem lowers blood pressure through calcium-channel blockade and also slows the heart rate. Used together, the combined effect tends to be a little larger than the medicine alone. Watch for dizziness on standing in the first couple of weeks, and tell your GP if it happens so your dose can be reviewed.
Evidence: Limited human data, based on case reports and a known mechanism.
Amber Does interact with Lisinopril?
Spirulina has a mild blood-pressure-lowering effect of its own, shown in human trials. Lisinopril lowers blood pressure by blocking the angiotensin-converting enzyme. Used together, the combined effect tends to be a little larger than the medicine alone. Watch for dizziness on standing in the first couple of weeks, and tell your GP if it happens so your dose can be reviewed.
Evidence: Limited human data, based on case reports and a known mechanism.
Amber Does interact with Losartan?
Spirulina has a mild blood-pressure-lowering effect of its own, shown in human trials. Losartan lowers blood pressure by blocking the angiotensin II receptor. Used together, the combined effect tends to be a little larger than the medicine alone. Watch for dizziness on standing in the first couple of weeks, and tell your GP if it happens so your dose can be reviewed.
Evidence: Limited human data, based on case reports and a known mechanism.
Amber Does interact with Ramipril?
Spirulina has a mild blood-pressure-lowering effect of its own, shown in human trials. Ramipril lowers blood pressure by blocking the angiotensin-converting enzyme. Used together, the combined effect tends to be a little larger than the medicine alone. Watch for dizziness on standing in the first couple of weeks, and tell your GP if it happens so your dose can be reviewed.
Evidence: Limited human data, based on case reports and a known mechanism.
Amber Does interact with Verapamil hydrochloride?
Spirulina has a mild blood-pressure-lowering effect of its own, shown in human trials. Verapamil lowers blood pressure through calcium-channel blockade and also slows the heart rate. Used together, the combined effect tends to be a little larger than the medicine alone. Watch for dizziness on standing in the first couple of weeks, and tell your GP if it happens so your dose can be reviewed.
Evidence: Limited human data, based on case reports and a known mechanism.
Additive anticoagulation
Amber Does interact with Acenocoumarol?
Spirulina has a mild antiplatelet signal in laboratory studies, but a human trial at a high dose found no change in clotting tests or platelet activity. Any effect on acenocoumarol is likely to be small. If you take acenocoumarol, keep your spirulina intake steady rather than starting or stopping suddenly, and tell your anticoagulation clinic what you take.
Evidence: Based on an established mechanism, with no direct study of this exact combination yet.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Amber Does interact with Warfarin sodium?
Spirulina has a mild antiplatelet signal in laboratory studies, but a human trial at a high dose found no change in clotting tests or platelet activity. Any effect on warfarin is likely to be small. If you take warfarin, keep your spirulina intake steady rather than starting or stopping suddenly, and tell your anticoagulation clinic what you take.
Evidence: Based on an established mechanism, with no direct study of this exact combination yet.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Immune-stimulant vs immunosuppressant (precautionary)
Amber Does interact with Ciclosporin?
Ciclosporin works by calming the immune system down, which is what stops your body rejecting a transplant or quietens an autoimmune condition. Spirulina has a genuine immune-stimulating effect, which in theory pulls in the opposite direction. There is no study of the two together, but because the stakes with a transplant or autoimmune disease are high, it is safer not to start spirulina while you take ciclosporin without first checking with your specialist team.
Evidence: Based on an established mechanism, with no direct study of this exact combination yet.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Amber Does interact with Tacrolimus?
Spirulina can stimulate parts of the immune system, which in theory works against a medicine like tacrolimus that is meant to suppress it. This has not been tested in people taking immune-suppressing medicines, so it is a cautious flag rather than a strong warning. If you take tacrolimus after a transplant or for an autoimmune condition, check with your specialist before starting spirulina.
Evidence: Based on an established mechanism, with no direct study of this exact combination yet.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
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.
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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.
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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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