NZ Formulary



What does it do?

Levothyroxine is used to add thyroid hormones to your body.

How should you take it?

Take levothyroxine regularly as directed with a glass of water. Take it on an empty stomach – one hour before or two hours after food.

What if you forget a dose?

Take the missed dose as soon as possible. If it is close to the time for your next dose, skip the missed dose and carry on as normal. Do not take two doses at the same time.

Can you take other medicines?

Some medicines available without a prescription may react with levothyroxine including:

  • antacids (e.g. Mylanta®), supplements containing calcium (e.g. Calci-tab®) or iron (e.g. Ferro-Tab®) - do not take these within four hours of levothyroxine.
  • iodine supplements (e.g. Iodine/Lugol’s solution®)

Tell your pharmacist or doctor about all medicines or treatments that you may be taking including vitamins, herbal products (e.g. kelp powder) or recreational drugs. Avoid foods such as seaweed or kelp that may contain iodine.

Important information continues on next page.

What side effects might you notice?

Side EffectsRecommended action

Chest pain, change in heartbeat


Heat intolerance, sweating

Restlessness, irritability, nervousness, tiredness

Hair loss or thinning

Changes in periods

Diarrhoea, nausea, vomiting, weight loss

Trouble sleeping

Tell your doctor

If you notice any other effects, discuss them with your doctor or pharmacist.

Other information:

  • Tell your doctor if you have heart problems, diabetes, osteoporosis (weak bones), or high blood pressure.
  • Tell your doctor if you are pregnant, planning to become pregnant, or breastfeeding.
  • Levothyroxine should not be used for weight loss.