Both are good options, and that surprises most people. Almost everyone gets handed the morning instruction at the pharmacy and never hears that night is even allowed. It is. A few studies suggest absorption is slightly better at night, probably because your gut isn’t moving things along as fast as it does first thing.

What decides it is your routine. If you take iron in the morning, or your first coffee happens before your feet hit the floor, night is easier. If you take minerals before bed, mornings win. The tool above works out which one collides with less of your day.

You absorb less of it. Food slows the tablet down and some of the dose never makes it in, which is why the empty stomach instruction exists in the first place.

Levothyroxine hangs around for about a week, so one rushed morning isn’t going to move your labs. It’s the pattern that matters. If breakfast is landing on top of your dose several times a week, the morning slot probably isn’t working for you, and night is worth asking your doctor about.

Thirty to sixty minutes covers most of them. That is the same window you wait before food, and it is the right answer for the large majority of what people take.

The exceptions are the ones that bind to the tablet: calcium, iron, soy, fiber supplements and antacids. Those want roughly four hours.

Calcium and iron have the strongest evidence behind them. Soy, fiber supplements, antacids, sucralfate and the cholesterol binders belong in the same group.

The ones people miss are the hidden sources. Tums is calcium carbonate. Most multivitamins carry calcium and often iron. Prenatals almost always carry iron. Almond and oat milk are nearly always fortified with calcium.

Coffee physically interferes with the tablet in your gut. In one study, espresso taken at the same moment lowered absorption by 25 to 57%.

That same study found no interference at all when the coffee came 60 minutes later. So coffee is not off limits, it just waits an hour. If that is never going to happen in your house, dose at night and drink it whenever you like.

It is the calcium in it, not the dairy itself. Calcium binds to the tablet and measurably lowers how much of it you absorb.

This applies to fortified plant milks too. Almond and oat milk are nearly always calcium fortified, so switching to those does not solve it.

Yes. That is already fine and you do not need to change anything.

Magnesium gets listed next to calcium and iron on most timing charts, but the evidence is much weaker. The only trial gave magnesium at the very same moment as levothyroxine and absorption fell 7 to 12%, with the citrate arm not even statistically significant. Nobody has tested a four hour gap because nobody has shown it needs one.

The binders are the clearest: cholestyramine, colesevelam, sucralfate, aluminium antacids, sevelamer, and the chelating antibiotics like ciprofloxacin and doxycycline. Those want about four hours.

Then there are the ones spacing will not fix. Acid blockers may lower absorption by raising your stomach pH, and oral estrogen raises the protein that carries thyroid hormone, which raises the dose you need. Both are worth a conversation with your doctor rather than a schedule change.

Two to four days. Biotin does not affect absorption at all, but it interferes with the assay most labs use to measure thyroid hormone.

It makes TSH read falsely low and free T4 and T3 read falsely high, which looks like an overactive thyroid on paper. Check the label on your B complex and any hair, skin and nails formula, because that is where most people are getting it without realising.

With a meal that has some fat in it, which by definition puts it outside the window with your medication anyway.

Vitamin D is not a binder, so it does not need the four hour separation. Just keep it out of the 30 to 60 minutes after your tablet, same as everything else.