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 evidence for its role in thyroid function is Grade A, with Zimmermann 2009 and Bath 2013 among the key references. Potassium iodide at 150 to 300mcg 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
Additive iodine load (thyroid toxicity)
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.
Additive thyroid suppression
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.
Antithyroid drug interference
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.
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.
Thyroid status destabilisation
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.
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.
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 methodologyWant this checked across everything you take?
This page checks the pairs you enter. The personalised Distil report goes further:
- the same graded, cited interaction check across your whole stack, not just the pairs you thought to type in
- where your current routine may be leaving you short of your goals
- the evidence-backed compounds worth adding, and the ones worth dropping
It's a paid report: £79, or £49 for the first 25 customers. The interactions check is one section of it, and you can read a real one in full before you buy.
See a real sample reportSomething missing?
If a supplement or medication you take isn't in our autocomplete, tell us. We go through what people flag every week and add what's missing.