Iodine and medications.
Iodine is in the Distil supplement database, evidence Grade A. The page below lists every medication we have explicitly assessed it against.
Iodine is the raw material for thyroid hormone, which in turn sets metabolic rate and supports cognition. Mild shortfall is becoming more common in the UK as dairy intake drops, and vegans are at higher risk because they miss the seaweed and dairy sources. The grade depends on where you are starting from. Correcting a documented iodine shortfall is Grade A, and that is what the strong evidence covers; if your intake is already adequate, the evidence that adding more improves thyroid function is Grade C. Pregnancy is the clear exception and stands on its own evidence, which is why the NHS recommendation below applies regardless. Zimmermann 2009 and Bath 2013 are among the key references. Potassium iodide at 150mcg a day covers most needs; the NHS recommends 140mcg a day in pregnancy, where iodine is critical for fetal brain development. The interactions are worth respecting. Iodine works with selenium for thyroid synthesis, but it can interfere with thyroid medication dosing, so your GP needs to know you are taking it. In Hashimoto's thyroiditis, high-dose iodine can worsen the autoimmune picture, so keep to physiological doses and monitor. The main risk at either extreme is thyroid disruption, so matching the dose to actual need matters more than taking more.
Below are the 5 documented pairs we have explicitly assessed for Iodine: 1 red and 4 amber. The pairs cluster around 4 mechanisms: Additive iodine load (thyroid toxicity), Additive thyroid suppression, Antithyroid drug interference, and Thyroid status destabilisation. 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 iodine load (thyroid toxicity)
Red Does interact with Amiodarone?
Amiodarone is itself an enormous iodine load, and around one in five people taking it develop a thyroid problem because of that. Adding an iodine supplement on top increases that risk and is not advised. Do not take iodine while you are on amiodarone unless a specialist has specifically told you to.
Evidence: Supported by human study data.
Additive thyroid suppression
Amber Does interact with Lithium carbonate?
Lithium can affect the thyroid and commonly causes an underactive thyroid or goitre over time. Iodine intake interacts with that effect, so taking an iodine supplement on top of lithium can add to the risk of thyroid problems. If you take lithium, do not start an iodine supplement without discussing it with your GP, and make sure your thyroid is being monitored.
Evidence: Supported by human study data.
Antithyroid drug interference
Amber Does interact with Carbimazole?
Carbimazole is used to calm an overactive thyroid. Taking an iodine supplement at the same time can work against it by giving the thyroid more raw material to make hormone, which may make your overactive thyroid harder to control. Iodine supplements are generally not advised while you are being treated for an overactive thyroid unless a specialist has told you otherwise.
Evidence: Supported by human study data.
Amber Does interact with Propylthiouracil?
Propylthiouracil is used to calm an overactive thyroid. Taking an iodine supplement at the same time can work against it by giving the thyroid more raw material to make hormone, which may make your overactive thyroid harder to control. Iodine supplements are generally not advised while you are being treated for an overactive thyroid unless a specialist has told you otherwise.
Evidence: Supported by human study data.
Thyroid status destabilisation
Amber Does interact with Levothyroxine?
Taking extra iodine while you are on levothyroxine can shift your thyroid status and may change how much levothyroxine you need. Most people on a stable dose do not need an iodine supplement, and large doses are best avoided unless your GP has advised one. If you do start iodine, ask your GP to recheck your TSH so your dose can be adjusted if needed.
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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