The information provided here is meant to give you a general idea about each of the medications listed below. Only the most general side effects are included, so ask your healthcare provider if you need to take any special precautions. Use each of these medications only as recommended by your healthcare provider, and according to the instructions provided. If you have further questions about usage or side effects, contact your healthcare provider.

Prescription Medications

Synthetic thyroxine (T4)

  • Levothyroxine (Synthroid, Levothroid, Levoxyl, Unithroid)

Synthetic triiodothyronine (T3)

  • Liothyronine (Cytomel)

Synthetic Thyroxine (T4)

  • Levothyroxine (Synthroid, Levothroid, Levoxyl, Unithroid)

Synthetic T4 is usually taken once a day. The dose of synthetic T4 is based on your age, weight, the condition of your heart, and the severity and duration of your hypothyroidism. Getting to the right dose can take time, as it is very individual and the range of the correct dosage is narrow. The dosage is gradually increased every 4-6 weeks until the blood levels of T4 and TSH are both in the normal range.

If you are elderly or have a heart condition, your doctor will start with a very low dose to give your body a chance to get used to the higher thyroid hormone level. After you have reached normal levels of T4 and TSH, your doctor may want to see you at least twice a year to make sure your levels continue to be in the normal range. Sometimes, thyroid blood levels can get higher or lower over time, making it necessary to increase or decrease the dosage of medicine.

You may begin to feel better within one to two weeks after starting medication, but often it can take longer. In fact, it may take three to six months after your blood levels are normal before you really feel well. Once this happens, you must continue to take synthetic T4, as hypothyroidism is not curable. You should take synthetic hormones for the rest of your life. Remember to take your thyroid medication on an empty stomach since food in the stomach will interfere with its absorption.

Once you start on a certain brand of synthetic T4, you should stay on that brand; the same dose of another brand may be absorbed differently in your body. If you change your dose or brand, you will be asked to have your blood levels of TSH, T3, and T4 checked about six weeks later.

Synthetic Triiodothyronine (T3)

  • Liothyronine (Cytomel)

Liothyronine is not prescribed as often as the T4 medicine, which is usually the choice of most physicians. This medication is often given to patients after their thyroid is removed surgically. It is sometimes prescribed along with levothyroxine.

Note

When taken at the proper dosage, there is little concern of side effects with synthetic T4 and synthetic T3. Both of these are forms of thyroid hormones, substances that are natural and needed in your body.

If you take too much of either of these synthetic hormones, it may cause the following problems:

  • Hyperthyroidism —Symptoms include nervousness, sweating, palpitations, insomnia, headache, alopecia , vomiting, muscle weakness, weight loss, or diarrhea .
  • Increased risk of heart attack, rapid heart rate (tachycardia) or irregular heart beats, chest pain ( angina ) or shortness of breath, especially if you have a previous history of heart disease
  • Increased loss of calcium from your bones, which can lead to osteoporosis

Special Considerations

Whenever you are taking a prescription medication, take the following precautions:

  • Take them as directed—not more, not less, not at a different time.
  • Do not stop taking them without consulting your healthcare provider.
  • Don’t share them with anyone else.
  • Know what effects and side effects to expect, and report them to your healthcare provider.
  • If you are taking more than one drug, even if it is over-the-counter, be sure to check with a physician or pharmacist about drug interactions.
  • Plan ahead for refills so you don’t run out.