Supplement · Grade A

Selenium and medications.

Every documented pair, every citation. Below: 1 documented pair grouped by mechanism.

Selenium is in the Distil supplement database, evidence Grade A. The page below lists every medication we have explicitly assessed it against.

Selenium is a trace mineral the body needs in small amounts, and UK soils are low in it, so moderate shortfall is common here. Its clearest job is helping convert thyroid hormone T4 into the active T3, which makes it especially relevant in hypothyroidism and Hashimoto's, and it also drives glutathione peroxidase, one of the body's antioxidant enzymes. Evidence is Grade A for thyroid and antioxidant roles and Grade B for immune function and male fertility, with Rayman 2012 as the standing review. Selenomethionine at 55 to 200mcg is the usual supplemental range; the upper safe limit is 400mcg a day and there is no reason to push past 200mcg from supplements. Going too high causes selenosis: hair loss, brittle nails and a garlic odour on the breath. On interactions, selenium pairs with iodine for thyroid work since both are needed, and anyone on anticoagulants should have it monitored. At sensible doses it is well tolerated, so more is not better here.

Below are the 1 documented pair we have explicitly assessed for Selenium: 1 green. The pairs cluster around 1 mechanism: Thyroid cofactor (beneficial). 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

Thyroid cofactor (beneficial)

Green Levothyroxine

Selenium and levothyroxine work together rather than against each other. Selenium is a building block the body needs to convert thyroid hormone into its active form, and in people with Hashimoto's it can lower thyroid antibodies. It does not change how much levothyroxine you absorb or how much you need, and good trials found no safety problem combining them. Keep your selenium to around 100 to 200 micrograms a day, since very high doses are harmful in their own right. We treat this pair as safe to combine.

PMID 11932302 · PMID 20883174 · PMID 38243784 · PMID 23844613 · BNF: Levothyroxine

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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For adults over 18. This tool gives evidence-graded information, not medical advice. Always discuss changes with your GP, especially if you take any medication, are pregnant, breastfeeding, or have a serious health condition.

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How we decide

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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Distil's interactions database is reviewed and updated every quarter. We grade evidence transparently and publish our methodology, including every database change, at /about/methodology. This tool is information, not a substitute for clinical judgement. If you take medication and supplements together, your GP or pharmacist can review your full regimen against your medical history. If you want a full personalised stack reasoned against this same database, the Distil report is the next step up.