A study in Clinical and translational science 2024, a crossover clinical trial in 15 healthy adults, looked at what happens when levothyroxine is taken together with two powdered magnesium salts, citrate and aspartate. The researchers found that thyroid hormone absorption decreased slightly, by about 7 to 12 per cent, when taken at the same time as these magnesium preparations dissolved in water.
The work focused on healthy people, not hypothyroid patients, but the question is a practical one. Many people taking levothyroxine also use magnesium for muscle, energy or general well-being. Understanding how they interact helps to better organise intake and to take care of the stability of thyroid function.
Study shows slightly reduced absorption of levothyroxine with magnesium
The trial was conducted at a single hospital site in Zurich. Each participant received three interventions on different days, separated by a washout of at least four weeks. At one visit they took levothyroxine alone, at another visit levothyroxine with magnesium aspartate, and at the third visit levothyroxine with magnesium citrate.
A single dose of 1 milligram of levothyroxine tablets was administered. Total thyroxine blood levels were then measured for six hours. The main objective was to compare the area under the curve, which reflects how much hormone is absorbed in that period. With magnesium aspartate the total exposure decreased by 12 percent. With magnesium citrate the reduction was 7 percent and did not reach statistical significance.
The authors consider the effect to be small and probably of little relevance in most patients. However, they point out that in people who need very fine control of thyrotropin, the TSH hormone, it is advisable to avoid taking levothyroxine at the same time as magnesium supplements or drugs.
Why magnesium can interfere with levothyroxine in the gut
Magnesium is a divalent cation. This means that it carries two positive charges and tends to form complexes with molecules that have opposite charges. Levothyroxine, which is a synthetic form of the thyroid hormone T4, can bind to these ions in the gastrointestinal tract.
When complexes form between magnesium and levothyroxine, some of the drug is no longer available for absorption through the intestinal wall. The result is a slightly smaller fraction of the hormone reaching the blood. This mechanism is similar to that described for other minerals such as calcium or iron, which are already known to interfere with levothyroxine if taken together.
The study used powdered formulations of magnesium aspartate and citrate, dissolved in water. The authors note that the magnitude of the interaction may vary with other formulations, such as tablets or capsules, and that further studies are needed to clarify this. Still, the practical message is clear: space levothyroxine and any magnesium supplementation over time.
Simple habits for combining magnesium and thyroid treatment
Those taking levothyroxine usually take it on an empty stomach, with water, and wait at least 30 minutes before eating breakfast. This habit facilitates a more stable absorption of the drug. If a magnesium supplement is also used, the wisest option is to reserve it for another part of the day, for example with lunch or dinner.
Separating doses by at least four hours reduces the likelihood of complexes forming in the gut. This is also recommended for other minerals that interfere with levothyroxine, such as calcium or iron. Keeping regular schedules and avoiding abrupt changes in medication and supplementation routine helps to make TSH tests easier to interpret.
In addition to the schedule, it is important to take care of the basics: a diet rich in vegetables, fruit, quality proteins and healthy fats, good hydration and appropriate physical activity. These pillars support both metabolism and muscle and nerve health, areas where magnesium plays a key role.
How Nutribiolite MAG-FUSION fits into a levothyroxine routine
MAG-FUSION is a magnesium supplement from Nutribiolite designed to support physiological processes such as muscle function, energy metabolism and nervous system balance. Although the specific formulation was not evaluated in the Zurich trial, it shares a central element with the study, the use of magnesium in highly bioavailable organic forms, such as citrate.
Organic magnesium salts, for example citrate, are generally better absorbed than cheaper inorganic forms such as oxide. This means that the same physiological effect can be achieved at lower doses and with less risk of digestive discomfort. This efficiency is one of the keys to well-designed magnesium supplements and sets them apart from generic formulations.
Clinical work suggests that magnesium citrate interferes less with levothyroxine absorption than magnesium aspartate, although the interaction still exists. This observation reinforces the idea of choosing forms of magnesium with good bioavailability and a favourable tolerance profile, and of paying attention to the timing of intake when combined with thyroid medication.
MAG-FUSION is presented as a tool for adults who already take care of their diet and physical activity and want additional physiological support with magnesium and selected vitamins. The absence of unnecessary additives and the use of well-absorbable magnesium salts offer an advantage over products that rely on less bioavailable forms and added excipients.
A well-absorbable magnesium supplement, free of unnecessary additives, intended for adults seeking to support muscles, energy and the nervous system.
Final summary, magnesium science and daily organisation
Clinical trial in healthy adults shows that magnesium can slightly reduce levothyroxine absorption. The effect is small, but enough to justify those dependent on this medication to separate magnesium supplementation over time.
Organising intake schedules, taking care with diet and choosing supplements with well-absorbable forms of magnesium and clean formulations makes it safer to take advantage of its physiological benefits. The aim is to support the body’s work, not to replace it.
This content is for information only and does not replace the advice of a healthcare professional.
Frequently asked questions
What did the study on magnesium citrate and levothyroxine show?
The trial in healthy adults found that taking levothyroxine together with magnesium citrate reduced thyroid hormone absorption by about 7 percent. This decrease was slight and did not reach statistical significance, but indicates that there is some interaction.
It is best to always separate magnesium from levothyroxine
The study data and clinical experience suggest that it is wise to separate the two by several hours. This reduces the formation of complexes in the gut and promotes more stable absorption of levothyroxine over time.
Why magnesium citrate is valued over other forms
Magnesium citrate is an organic salt with good bioavailability, which means it is efficiently absorbed by the body. Compared to less soluble forms, such as magnesium oxide, it generally offers better utilisation and less risk of digestive discomfort at comparable doses.
It may make sense to use MAG-FUSION if I take levothyroxine.
It may make sense when you are looking for physiological support with well-absorbable magnesium and a clean formula. The key is to respect a margin of several hours between levothyroxine and supplementation, and to maintain a stable routine to facilitate the interpretation of thyroid function tests.
What other habits help thyroid care and mineral balance?
A varied diet, rich in vegetables, fruits, legumes and quality protein, helps to cover minerals and vitamins involved in metabolism. Regular eating and resting schedules, good hydration and moderate physical activity also help hormonal balance and the body’s handling of magnesium.
