Levothyroxine
Also known as: Eltroxin, Thyroid hormone
What it's for
Levothyroxine replaces the thyroid hormone your body is not making enough of. It treats an underactive thyroid (hypothyroidism), which can cause tiredness, weight gain, and feeling cold.
Comes as: Tablets
How to take it
- Adults: Dose varies - your doctor will find the right dose for you through blood tests.
- Take it first thing in the morning on an empty stomach.
- Wait 30 minutes before eating or drinking anything except water.
- Take it at the same time each day.
Doses here are typical. Always follow the instructions from your prescriber or on the packet — they come first.
Common side effects
- Side effects usually mean the dose is too high or too low
- Too much: fast heartbeat, sweating, weight loss, feeling anxious
- Too little: tiredness, weight gain, feeling cold
The leaflet inside the packet lists all known side effects.
Important safety points
- Take it the same way every day for consistent levels
- Some medicines and foods affect absorption - take other medicines at least 4 hours apart
- Do not stop taking it without medical advice
- You will need regular blood tests to check your levels
Get medical help urgently if…
- You have chest pain or a very fast heartbeat
- You feel very unwell with severe tiredness
- You have difficulty breathing
Call NHS 111 for urgent advice, or 999 if someone is seriously unwell.
Before you act on anything here
This page is general information, written to help you understand — it is not personal medical advice and it cannot tell you what is right for you. Talk to your own GP, pharmacist or nurse about your own health.
- Need help now but it's not an emergency? Call NHS 111 or use 111.nhs.uk.
- Emergency? Call 999 or go to A&E.