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Levothyroxine

Medication thyroid hormone hormonal
Aka: Euthyrox, Synthroid, T4
Brands seen in Singapore: Euthyrox, Eltroxin, Thyrocord, Rovexine, Thyrosit
Not medical advice. Check with your doctor or pharmacist before you start, stop or change the timing of anything you take.
How to use
What it’s for
An underactive thyroid (hypothyroidism) — NHS, HealthHub
When to take
Morning, once a day, at the SAMe time each day
Take with
An empty stomach, 30–60 min before food, coffee or medicines
Pros & cons
Pros
  • NHS: can ease tiredness, weight gain and low mood
  • HealthHub: generally well tolerated, side effects mild
  • NHS: usually one dose a day, taken long term
Cons
  • NHS: most side effects come from too high a dose
  • US label: boxed — not for obesity or weight loss
  • NHS: regular blood tests needed to check the dose
Sources
  1. HSA — Listing of Registered Therapeutic Products (data.gov.sg open dataset, 5,511 rows, full CSV pulled once via the datastore_search API and filtered locally) · read 2026-08-27
    what it says
    “Forensicclassification = 'Prescription Only' for all 16 levothyroxine rows: EUTHYROX 25/50/75/100 mcg, Eltroxin 50/100 mcg, THYROCORD 25/50/75/100 MCG, ROVEXINE 25/50/75/100 MCG, THYROSIT TABLET 100 mcg, plus LEVOTHYROXINE SODIUM FOR INJECTION 500 mcg/vial”
  2. NHS Medicines A-Z — Levothyroxine: what it is used for (page dateModified 11 Aug 2026) · read 2026-08-27
    what it says
    “Levothyroxine is mainly used to treat an underactive thyroid (hypothyroidism). Levothyroxine can help with symptoms of an underactive thyroid including: tiredness · weight gain · low mood”
  3. NHS Medicines A-Z — Levothyroxine: how and when to take it · read 2026-08-27
    what it says
    “take it on an empty stomach 30 to 60 minutes before your first meal of the day, any drink with caffeine, such as tea or coffee, or any other medicine … You'll usually take it once a day.”
  4. NHS Medicines A-Z — Levothyroxine: dosage · read 2026-08-27
    what it says
    “How much you need to take depends on your thyroid hormone levels, any other conditions you may have and your age … Your doctor may prescribe a low dose to start with and increase it gradually.”
  5. NHS Medicines A-Z — Levothyroxine: side effects · read 2026-08-27
    what it says
    “Common side effects of levothyroxine include: difficulty sleeping (insomnia) · headaches · feeling anxious · sweating · hair loss … Most side effects usually happen when the dose is too high.”
  6. NHS Medicines A-Z — Levothyroxine: blood tests and monitoring · read 2026-08-27
    what it says
    “You'll have regular blood tests to check you're on the right dose of levothyroxine. Being on the wrong dose can cause side effects, such as feeling or being sick, diarrhoea, headaches or problems sleeping.”
  7. NHS Medicines A-Z — Levothyroxine: who can and cannot take it · read 2026-08-27
    what it says
    “levothyroxine is not suitable for everyone. For example, it may not be suitable if: you have an overactive thyroid · you have diabetes · you have a condition that affects your adrenal glands · you have a heart condition”
  8. NHS Medicines A-Z — Levothyroxine: pregnancy and breastfeeding · read 2026-08-27
    what it says
    “Levothyroxine can be taken during pregnancy if needed. If you need to take levothyroxine while you're pregnant, you may need more blood tests to check your thyroid hormone levels and make sure you're taking the right dose.”
  9. NHS Medicines A-Z — Levothyroxine: taking it with other medicines and herbal supplements · read 2026-08-27
    what it says
    “medicines to reduce the amount of acid in your stomach, such as omeprazole … antacids and other indigestion treatments · calcium and iron supplements … St John's wort · biotin (vitamin B7) as it can affect your thyroid tests”
  10. HealthHub (MOH Singapore / Pharmaceutical Society of Singapore) — Levothyroxine medication information leaflet, last reviewed 21 May 2026 · read 2026-08-27
    what it says
    “Take Levothyroxine in the morning on an empty stomach, at least 30 minutes before the first food or drink of the day … Do not stop taking your medication or change the brand of levothyroxine without informing your doctor.”
  11. HealthHub — Levothyroxine leaflet: food and medicines to avoid, tolerability · read 2026-08-27
    what it says
    “Avoid food, drinks, medications or supplements that are high in calcium, iron or magnesium 2 to 4 hours before and after taking Levothyroxine … Generally, this medication has been well tolerated. Side effects usually have been mild”
  12. FDA DailyMed — SYNTHROID (levothyroxine sodium) tablets, AbbVie Inc., SPL v1537, effective 20 Feb 2024: dosing footnote · read 2026-08-27
    what it says
    “Dosages greater than 200 mcg/day are seldom required. An inadequate response to daily dosages greater than 300 mcg/day is rare and may indicate poor compliance, malabsorption, drug interactions, or a combination of these factors”
  13. FDA DailyMed — SYNTHROID prescribing information: boxed warning · read 2026-08-27
    what it says
    “WARNING: NOT FOR TREATMENT OF OBESITY OR FOR WEIGHT LOSS — Thyroid hormones, including SYNTHROID, either alone or with other therapeutic agents, should not be used for the treatment of obesity or for weight loss.”
  14. FDA DailyMed — SYNTHROID prescribing information: section 2.1 Important Administration Instructions · read 2026-08-27
    what it says
    “Administer SYNTHROID as a single daily dose, on an empty stomach, one-half to one hour before breakfast. Administer SYNTHROID at least 4 hours before or after drugs known to interfere with SYNTHROID absorption”
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Updated 2026-08-29. Every line above traces to a numbered source. Kozen-X is not a medical device and does not give medical advice. It lists what published sources have written down — nothing more. A pair not listed is unrecorded, not cleared. Before you start, stop or re-time anything, talk to your doctor or pharmacist.