Euthyrox contains levothyroxine, a synthetic thyroid hormone. It is used to replace thyroid hormone when the thyroid gland is underactive — the most common reason being hypothyroidism. It comes in 25, 50, 75 and 100 microgram tablets, and is taken once daily, usually for life.
What is Euthyrox?
Euthyrox is Schedule 3 in South Africa:
| Product | Contains |
|---|---|
| Euthyrox 25 µg | Levothyroxine sodium 25 micrograms |
| Euthyrox 50 µg | Levothyroxine sodium 50 micrograms |
| Euthyrox 75 µg | Levothyroxine sodium 75 micrograms |
| Euthyrox 100 µg | Levothyroxine sodium 100 micrograms |
Note the unit: micrograms (µg), not milligrams. A microgram is a thousandth of a milligram, and levothyroxine is one of the few medicines dosed this finely. That precision is the point — small differences in dose produce real differences in how you feel.
Levothyroxine is a synthetic version of thyroxine (T4), the main hormone the thyroid gland produces. The body converts T4 into the more active T3 in the tissues, as needed.
Thyroid hormone sets the metabolic pace of essentially every tissue — heart rate, body temperature, digestion, growth, brain function and how quickly you use energy. When there is too little, everything slows: fatigue, weight gain, feeling cold, constipation, dry skin, hair thinning, slowed thinking, low mood and heavy or irregular periods.
Levothyroxine is replacement, not treatment. It does not repair the thyroid; it supplies what the gland no longer makes. That is why it is usually taken for life, and why stopping it means the symptoms return over weeks.
Two things follow from how it works, and both matter:
- It is slow. Levothyroxine has a long half-life of about a week, so changes take time. Blood tests are done about 6 to 8 weeks after starting or changing a dose — testing sooner gives a misleading result.
- Small changes matter. Dose adjustments are usually made in 25 µg steps, guided by your TSH blood level rather than by how you feel alone.
What is Euthyrox commonly used for?
- Hypothyroidism (underactive thyroid) — the main use, whatever the cause.
- Hashimoto’s thyroiditis, an autoimmune condition and the most common cause of hypothyroidism.
- After thyroid surgery, where part or all of the gland has been removed.
- After radioactive iodine treatment for an overactive thyroid.
- Congenital hypothyroidism, present from birth — where prompt treatment is critical for normal brain development.
- Goitre, to reduce thyroid enlargement in some cases.
- Thyroid cancer, at higher doses, to suppress TSH after treatment.
- Subclinical hypothyroidism, in some circumstances.
Hypothyroidism is common in South Africa and frequently undiagnosed, because the symptoms — tiredness, weight gain, feeling cold, low mood — are easily attributed to other things. It is diagnosed with a simple blood test.
You will not feel better immediately. Improvement usually begins within a couple of weeks, but full benefit takes six to eight weeks or longer. That gap catches people out, and it is a common reason someone concludes the medicine is not working.
How Euthyrox fits into this medicine category
| Group | Examples | Role |
|---|---|---|
| Thyroid hormone replacement | Levothyroxine (Euthyrox, Eltroxin) | Underactive thyroid |
| Antithyroid medicines | Carbimazole, propylthiouracil | Overactive thyroid — the opposite problem |
| Beta-blockers | Propranolol | Symptom control in overactive thyroid |
| Diabetes medicines | Metformin, semaglutide | Blood glucose — unrelated to thyroid |
| Corticosteroids | Prednisone | Adrenal and inflammatory conditions |
Levothyroxine is not a weight-loss medicine. It restores normal metabolism in someone deficient, and weight often settles as a result — but taking it without a deficiency does not cause healthy weight loss, and doing so causes the dangerous effects of an overactive thyroid: heart rhythm disturbance, bone loss and muscle wasting. See the endocrine and diabetes medicines hub.
What to check before using Euthyrox
Take it on an empty stomach, first thing in the morning, with water, and wait 30 to 60 minutes before eating or drinking anything else. This is the single most important instruction on this page. Food — coffee especially — substantially reduces absorption, and inconsistent timing is one of the commonest reasons levels stay unstable.
Separate it by at least four hours from:
- Calcium supplements and calcium-containing antacids.
- Iron supplements.
- Magnesium, including Slow-Mag, and multivitamins containing minerals.
- Antacids generally.
These bind levothyroxine in the gut and can substantially reduce how much you absorb — a frequent and easily missed cause of treatment appearing to fail.
Be consistent about the brand. Different levothyroxine products can differ slightly in absorption. If your brand changes, mention it, as a repeat blood test may be sensible.
Tell your doctor or pharmacist if you:
- Have heart disease, angina or a rhythm disorder. Treatment is usually started at a low dose and increased slowly, because raising metabolism increases the heart’s workload.
- Are elderly, where the same caution applies.
- Have adrenal insufficiency (Addison’s disease). This must be treated first — starting levothyroxine before corticosteroid replacement can precipitate an adrenal crisis.
- Have diabetes. Levothyroxine can raise blood sugar, and diabetes treatment may need adjusting.
- Have osteoporosis, or are postmenopausal — over-replacement accelerates bone loss.
- Are pregnant, or planning pregnancy. Requirements rise substantially in pregnancy — often by 25 to 50% — and usually in the first trimester. Untreated hypothyroidism in pregnancy affects fetal brain development, so tell your doctor as soon as you know, and expect more frequent testing.
- Take warfarin, whose effect levothyroxine increases.
- Take amiodarone, lithium, phenytoin, carbamazepine, rifampicin, oestrogen or sertraline, all of which affect thyroid hormone levels or requirements.
Expect regular blood tests — TSH, usually 6 to 8 weeks after any change and then periodically.
Possible cautions and when to ask a pharmacist or doctor
Correctly dosed, levothyroxine causes no side effects — it is replacing a hormone you should have. Symptoms almost always mean the dose is too high or too low, which is a useful thing to know.
Signs the dose may be too high (over-replacement, mimicking an overactive thyroid):
- Palpitations, a fast or irregular heartbeat.
- Tremor, anxiety, restlessness or irritability.
- Difficulty sleeping.
- Sweating, or intolerance of heat.
- Unintended weight loss.
- Diarrhoea.
- Muscle weakness or cramps.
Seek medical advice promptly for these, and urgently for chest pain, a markedly irregular heartbeat or fainting.
Signs the dose may be too low: continuing tiredness, weight gain, feeling cold, constipation, dry skin and low mood.
Also contact your doctor if:
- You develop a rash, or swelling of the face or lips.
- You become pregnant.
- You start or stop any other medicine or supplement, particularly those listed above.
- You have worsening angina or new chest pain.
- Symptoms persist despite a normal TSH — worth discussing rather than assuming nothing more can be done.
Do not stop taking it because you feel well. Feeling well is the medicine working. Do not adjust the dose yourself, and do not double a missed dose — take it as soon as you remember that day, or skip it and continue normally.
Related medicine guides
Frequently asked questions
What is Euthyrox used for? Replacing thyroid hormone when the thyroid is underactive — hypothyroidism, Hashimoto’s thyroiditis, after thyroid surgery or radioactive iodine, and congenital hypothyroidism. It contains levothyroxine.
What is Euthyrox 100 used for? 100 micrograms is a common maintenance strength. The right dose is set by your TSH blood level, not by symptoms alone.
How should I take it? On an empty stomach, first thing in the morning with water, waiting 30 to 60 minutes before eating or drinking anything else. Food and coffee substantially reduce absorption.
How long before I feel better? Improvement usually begins within a couple of weeks, but full benefit takes six to eight weeks or longer.
Can I take it with my calcium or iron tablets? Not at the same time. Separate them by at least four hours — they bind levothyroxine and reduce absorption significantly.
Is it a weight-loss medicine? No. It restores normal metabolism in someone deficient. Taking it without a deficiency causes heart rhythm problems, bone loss and muscle wasting.
Do I need to take it forever? Usually yes. It replaces a hormone your thyroid no longer makes, and symptoms return within weeks of stopping.
What if I become pregnant? Tell your doctor immediately. Requirements rise substantially, often in the first trimester, and untreated hypothyroidism affects fetal brain development.