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Levothyroxine (LEE voe thy ROX een) is thyroid hormone medicine. Brand names for this medicine include Synthroid®, Levoxine®, Levothroid® and Levoxyl®. Thyroid medicine is used when the thyroid gland does not make enough thyroid hormone (hypothyroidism). It is a man-made medicine that replaces the hormone the thyroid gland naturally makes. Your child may take the medicine for several weeks before you notice a change in his symptoms. (See Helping Hand HH-I-343, Hypothyroidism.)

How to Give This Medicine

Mother and child getting prescription from a pharmacist

  • Read the label carefully. Make sure you give your child the right dose. It is easy to confuse the different dosage forms and strengths.

  • Give the exact dose the doctor ordered.

  • Stay with your child until he or she has swallowed the dose of medicine.

  • Wash and dry your hands before and after giving this medicine.

  • Ask your pharmacist, nurse or doctor before crushing this medicine.

  • For patients who cannot swallow pills, including babies discharged from the NICU, you can crush the pill and mix with 0.2 mL sterile water, breast milk or formula.  Draw up the dose with a needleless oral syringe and place in baby’s cheek (see Helping Hand HH-I-346, Congenital Hypothyroidism).  Do not put the medicine in the baby’s bottle.

  • It is very important to give the medicine every day as ordered, even if your child is feeling fine. Do not change doses or stop the medicine without talking to your child’s doctor.

If You Forget to Give a Dose

If you forget to give a dose of this medicine, give it as soon as possible, even if it is as much as a whole day late. If you have any questions about this or if you have missed more than 1 dose, check with your child’s doctor.

Drug-Food Interactions

Levothyroxine works best when the stomach is empty. This medicine should not be taken with the following foods or supplements (they make the medicine harder to absorb):

  • Soy protein products

  • Asparagus

  • Cabbage

  • Peas

  • Turnip greens

  • Broccoli

  • Spinach

  • Brussels sprouts

  • Lettuce

Levothyroxine should be given 3 to 4 hours after your child takes any of these supplements:

  • Iron supplements

  • Calcium supplements

  • Antacid supplements

Signs of not enough medicine:

  • Leg cramps

  • Coldness

  • Weight gain

  • Problems sleeping

  • Sweating

  • Constipation

  • Muscle aches

  • Decreased energy level

Signs of too much medicine:

  • Chest pain

  • Shortness of breath

  • Weight loss

  • Poor sleep

  • Dry, puffy skin

  • Diarrhea

  • Tremors

  • Headache

  • Fast or irregular heart rate

  • Nervousness

  • Decreased exercise tolerance

  • Feeling hot all the time

If your child is having any side effects that continue or are very bothersome, call his doctor. The dosage might need to be changed. Never change the amount of medicine yourself. If your child develops a skin rash, stop giving the medicine and call the doctor.
Call for emergency help if your child has any of these signs of an allergic reaction: trouble breathing, swelling of tongue, swelling of hands, feet or ankles.

Other Advice about the Medicine

  • Ask your pharmacist for 2 labeled bottles of medicine if your daycare provider or school nurse will be giving this medicine.

  • Make sure all refills are the same brand. Do not use the generic form of this medicine without checking with your doctor or pharmacist first.

If you carry medicine in your purse, keep it in its childproof bottle. Keep your purse out of the reach of children.

  • Bring all your child’s medicines with you in the original bottles whenever the child sees a doctor. This helps the doctors who may not know your child.

  • Learn the name, spelling and dose of this medicine. You will need to know this information when you call your doctor or pharmacist. Teach it to your child when he is old enough to learn it.

  • If your child takes too much of this medicine, or if someone else takes this medicine, first call the Central Ohio Poison Center at 1-800-222-1222 (TTY 614-228-2272). They will tell you what to do.

  • The doctor has prescribed this medicine for your child only. Do not give it to anyone else.

  • It is important to keep a record of when the medicine is given. You may use a calendar or the Helping Hand: Medication Record, HH-V-1.

  • Tell your child’s dentist your child is taking this medicine and the reason why.

  • Store the medicine bottle at room temperature. Dampness or heat can cause the medicine to break down.

  • Do not give medicine that has expired.

  • If your child has heart problems, this medicine can increase chest pain or shortness of breath when he is very active. If he develops these symptoms, call his doctor.

Make sure your child has regular checkups with his doctor to check his progress and be sure he is on the correct dose of medicine.

Levothyroxine (PDF) 

HH V-240 6/11, Revised 3/17 Copyright 2011, Nationwide Children's Hospital