You can take both iron and levothyroxine, but not at the same time. Iron binds to thyroid hormone in your stomach and blocks its absorption, so the FDA prescribing information says to take them at least 4 hours apart. The simplest plan is levothyroxine first thing in the morning and iron later in the day.
Medical disclaimer: This article is general information about medication timing and is not medical advice. Always consult your doctor or pharmacist for guidance specific to your medications.
Why iron and levothyroxine clash
Levothyroxine is absorbed in a narrow window in your gut, and it is fussy about company. Iron is one of the strongest offenders. The FDA label explains that "ferrous sulfate likely forms a ferric-thyroxine complex," a fancy way of saying the iron grabs the thyroid hormone and forms a clump your body cannot absorb well.
This is not a small effect. In a 1992 study in the Annals of Internal Medicine, 14 people with hypothyroidism took ferrous sulfate together with their levothyroxine for 12 weeks. Their average TSH, the lab marker that rises when thyroid treatment is falling short, climbed from 1.6 to 5.4, and 9 of the 14 felt more hypothyroid symptoms like fatigue and cold intolerance. In short, taking them together can quietly undertreat your thyroid.
The 4-hour rule and the easy schedule
The fix is timing, not stopping either one. Take levothyroxine on an empty stomach, then keep iron at least 4 hours away.
| Time | What to take |
|---|---|
| Morning, empty stomach | Levothyroxine, then wait 30 to 60 minutes before eating |
| Lunch or dinner | Iron supplement, at least 4 hours after levothyroxine |
| If you take both at night | Still separate them by 4 hours, and keep the order consistent |
Taking levothyroxine in the morning and iron with dinner gives you a wide, safe gap without much effort. The MedlinePlus patient guidance similarly stresses taking levothyroxine on an empty stomach and keeping supplements separate.
What counts as "iron"
It is not only the obvious iron pill. Watch for iron hidden in multivitamins, prenatal vitamins, and some greens or fortified products. If a supplement lists iron or ferrous sulfate, fumarate, or gluconate, it belongs in the 4-hour-away group. When in doubt, check the label or ask your pharmacist.
Signs your timing may be off
If iron has been creeping into the same hour as your levothyroxine, you might notice the symptoms of an underactive thyroid returning: tiredness, feeling cold, dry skin, constipation, or weight changes. These are the same signals the study above tracked. If you have them, do not adjust your dose yourself. Tell your prescriber, who may check your TSH and confirm your schedule.
For the full picture of which supplements to separate, see our guide on vitamins that interfere with thyroid medication. It also helps to nail down the best time to take levothyroxine and, if you slip up, what to do after a missed dose of levothyroxine.
How Pillo keeps the gap honest
The hard part is not knowing the 4-hour rule, it is remembering it every single day across two different times. That is precisely the kind of spacing a reminder can hold for you.
With Pillo, you can set a morning alarm for levothyroxine and a separate later alarm for iron, each persisting until you confirm it, so the two never drift back together. You can download Pillo on Google Play to keep your thyroid and iron doses safely spaced.
Frequently Asked Questions
Can I take iron and levothyroxine at the same time?
No. Iron binds levothyroxine in the gut and reduces how much you absorb. The FDA label says to separate them by at least 4 hours. Taking them together can let your thyroid become undertreated over time.
How long should I wait between levothyroxine and iron?
At least 4 hours. The easiest approach is levothyroxine first thing in the morning on an empty stomach and iron with lunch or dinner, which puts many hours between them while still letting both work.
What happens if I accidentally took them together once?
A single overlap is not an emergency. Go back to spacing them by 4 hours going forward. If overlaps have happened for weeks, mention it to your prescriber, who may check your TSH, since a 1992 study showed combined use can raise TSH and bring back hypothyroid symptoms.
Does the type of iron matter?
The interaction applies broadly to oral iron salts like ferrous sulfate, fumarate, and gluconate, and to iron hidden in multivitamins and prenatal vitamins. Any of them should be kept 4 hours away from levothyroxine. Check supplement labels for iron content.
Can I just take my levothyroxine at night to avoid my morning iron?
Possibly, but the rule is the same either way: keep a 4-hour gap and stay consistent. If you want to switch your levothyroxine to night, talk to your prescriber first so your TSH can be rechecked after the change.
The other big mineral interactions work the same way. See calcium and levothyroxine and magnesium and levothyroxine.
Medical disclaimer: This information is general and educational. It is not a substitute for professional medical advice and cannot account for your health history. Always consult your doctor or pharmacist before changing how or when you take your medications.
