Levothyroxine: How to Take It — With Coffee, Breakfast and Calcium?

Levothyroxine is absorbed mainly in the small intestine (the jejunum and ileum), and the acidic environment of the stomach helps the molecule reach a form that can be absorbed. Food, fibre, some drinks and metal ions can bind the drug molecule or alter the speed of gastric emptying, so that a smaller part of it reaches the blood. In practice this means the same tablet can give a slightly higher or slightly lower hormone concentration depending on the circumstances.

This result has direct practical significance: anything that reduces stomach acidity (chronic gastritis, H. pylori infection, proton pump inhibitor drugs) can increase the requirement for levothyroxine. We describe proton pump inhibitors in our knowledge base. TSH results that “will not stabilise” despite regular intake of the drug are therefore worth discussing with the doctor also from the point of view of the stomach and intestines.

The practical rule that follows is simple: swallow the drug with water and put coffee (including espresso and coffee with milk) off for 30–60 minutes — the study suggests that coffee drunk an hour after the tablet did not change absorption compared with water alone. It is worth remembering that the effect of coffee was smaller than that of fibre (bran proved the stronger interferer), and that the result concerned two 100 µg tablets taken once in a test, not regular use. If someone has for years drunk coffee together with the drug and has a stable, normal TSH, that does not mean they must suddenly change habits — but any change (adding or stopping coffee with the tablet) is worth treating as a change in the conditions of treatment and followed up with a TSH check.

Both studies lead to the same conclusion from different sides: a meal reduces levothyroxine absorption (mean TSH rises), but if someone truly cannot keep to fasting, this can be compensated for — under a doctor’s supervision, by increasing the dose and monitoring TSH. The worst solution is irregularity: once fasting, once with breakfast, once with coffee — then TSH fluctuates for no clear reason. Choose one way and stick to it.

The mechanism is chemical: calcium ions (and those of iron, magnesium and aluminium) bind thyroxine molecules in the gut and form complexes that are hard to absorb. For this reason calcium, iron, magnesium, multivitamins with minerals and drugs that neutralise stomach acid are worth taking with a clear gap from levothyroxine — in clinical practice about 4 hours is usually advised, although this is not a value derived from the single study cited here. We write about specific data for iron in a separate article on iron and levothyroxine. Often overlooked sources of calcium are also milk, yoghurt and fortified products, and sources of fibre — bran and psyllium-type supplements; these too can interfere with absorption if eaten together with the tablet.

The data are consistent with Centanni’s result: drugs that reduce acidity can raise TSH in people treated with levothyroxine. This is not a reason to stop the heartburn drug yourself — PPIs are important in reflux and peptic ulcer disease — nor to raise the levothyroxine dose yourself. Sensible practice is a TSH check a few weeks after starting or ending long-term PPI treatment and a discussion of the result with the doctor; if needed, the dose is adjusted or another form of the drug is considered. We write about other consequences of long-term reduction of acidity in our article on PPIs and deficiency of magnesium and vitamin B12.

The result seems to contradict the Bach-Huynh study, in which bedtime intake gave a higher TSH than morning fasting intake. The two studies differ in design, population and manner of taking the drug, and the available abstracts do not allow us to decide where the discrepancy comes from (one possibility is a different gap since the last meal before sleep). There are two practical conclusions. First, evening intake is a real alternative for people who find it hard to keep a gap before breakfast and coffee in the morning — provided that several hours (usually at least 3) have passed since the last meal. Second, changing the time from morning to evening may shift TSH, so after the change it needs to be checked after 6–8 weeks and the dose corrected if necessary.

The same goes for softgel capsules: in an open-label study of 47 patients after total thyroidectomy who were taking PPIs, switching from a tablet to a softgel capsule at the same dose was associated with a significant fall in TSH within 12 weeks (on average by 0.68 mIU/L) and a rise in hormone concentrations (Sachmechi et al., 2023), which suggests that absorption from the capsule is less sensitive to reduced stomach acidity. These forms can therefore be a good idea for people in whom TSH is hard to stabilise despite the correct manner of taking the drug, and for people on PPIs or with stomach disease — but the decision to change the preparation is the doctor’s, and the evidence comes from small, mostly open-label studies.

Levothyroxine is available in many brands and generic preparations. Although they meet equivalence requirements, clinical reviews point out that even small differences between preparations (including excipients) can cause marked changes in TSH, particularly in older people, in pregnancy and in children. The authors of a 2019 review (Benvenga and Carlé) advise staying on the same preparation where possible and, after it is changed, checking TSH and adjusting the dose if necessary. The review was financially supported by Merck, the maker of one of the levothyroxine preparations, which is worth bearing in mind when judging its conclusions, although checking TSH after a change of brand is widely accepted practice.

In practice: if the pharmacy has dispensed a different brand from usual, check the name on the packaging, ask the pharmacist about the differences and tell your doctor about the change. Ordering a follow-up TSH after 6–8 weeks is a sensible safeguard. If your doctor recommends a specific brand, the prescription can be marked as not permitting substitution. If symptoms of hormone excess or deficiency appear after the change of preparation (palpitations, trembling, or sleepiness, feeling cold, constipation), do not wait for the next scheduled visit.

The greatest value in levothyroxine treatment is not the ideal hour but repeatability. The drug works best when we take it every day under the same conditions and the dose has been chosen precisely for them. Coffee, breakfast and calcium do not invalidate treatment — but any change in how they are arranged relative to the tablet alters absorption enough for TSH to shift. A good habit is therefore to agree a routine with your doctor, stick to it and have TSH checked after every significant change.