Prescription requiredThyroid hormone replacement

Lethyrox 12.5 — Side Effects & Warnings

Known side effects of Lethyrox 12.5 include Palpitations,fast heart rate,anxiety,restlessness,tremor,headache,insomnia,increased sweating,heat intolerance,diarrhoea,weight loss,menstrual irregularities. Not everyone experiences these side effects.

Medically reviewed by Dr. Balaji Krishnan, MBBS · Updated August 2026

Common Side Effects

Palpitations
fast heart rate
anxiety
restlessness
tremor
headache
insomnia
increased sweating
heat intolerance
diarrhoea
weight loss
menstrual irregularities

This is not an exhaustive list. Consult your doctor if you notice any unusual symptoms.

Important Warnings

Use under medical supervision with regular TSH/T4 monitoring. Overtreatment can cause hyperthyroidism, arrhythmias, angina and bone loss/osteoporosis. Use caution in elderly and in patients with heart disease, hypertension, adrenal insufficiency (should be treated first), and diabetes (may alter glucose control). Not for weight loss/obesity management. Seek urgent care for chest pain, severe palpitations or breathlessness.

Drug Interactions

Lethyrox 12.5 may interact with the following:

Calcium salts
iron salts
antacids containing aluminium/magnesium
sucralfate
cholestyramine/colestipol
sevelamer (reduce absorption); proton pump inhibitors and dietary fibre/soy products may reduce absorption; warfarin (increased anticoagulant effect)
antidiabetic medicines (dose adjustment may be needed)
amiodarone
carbamazepine
phenytoin
rifampicin
sertraline (may alter thyroid hormone levels)
oestrogens/oral contraceptives (may increase requirement)

Always tell your doctor about all medicines you are taking, including over-the-counter drugs and supplements.

Pregnancy Safety

Generally safe (often required in pregnancy); dose adjustment and close monitoring needed—consult doctor

Alcohol Interaction

Use with caution; alcohol does not directly interact but may worsen symptoms or affect adherence—follow medical advice

Habit Forming

Storage

Store below 25°C in a dry place, protected from light and moisture. Keep in original blister/strip and out of reach of children.

Lethyrox 12.5 — Safety Summary

Composition: Levothyroxine sodium 12.5 mcg tablet
Prescription: Required (Rx)
Pregnancy: Generally safe (often required in pregnancy); dose adjustment and close monitoring needed—consult doctor
Alcohol: Use with caution; alcohol does not directly interact but may worsen symptoms or affect adherence—follow medical advice
Habit forming: No

Lethyrox 12.5 — Safety FAQs

What should I do if I experience side effects?

Mild side effects often resolve on their own. If side effects are severe or persistent, stop the medicine and consult your doctor immediately.

Are all listed side effects common?

No. Some side effects are common while others are rare. Not everyone experiences side effects. Consult your doctor if you are concerned.

Can I take this medicine with other drugs?

Some medicines interact with each other. Always inform your doctor about all medicines you are currently taking.

When should I seek emergency help?

Seek immediate medical attention if you experience severe allergic reactions (difficulty breathing, swelling of face/throat), chest pain, or any life-threatening symptoms.

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Safety disclaimer

This information is for educational purposes only and is not a substitute for professional medical advice. If you experience severe side effects, seek medical attention immediately.

Lethyrox 12.5 — Side Effects & Warnings

Medically reviewed by Dr. Balaji Krishnan, MBBS · Updated August 2026