Side Effects and Complications

Luckily, drugs for hypothyroidism tend not to cause many side effects. The main problem with taking thyroid replacement occurs when you take too little or too much of the drug. Too much, and you could become hyperthyroid, which means you'll feel jittery, anxious, and short of breath, and have trouble sleeping. You may also be at risk for osteoporosis since you're speeding up the turnover of bone. Too little, and you'll continue experiencing the symptoms of hypothyroidism. The key to avoiding that problem is finding the perfect dosage, which is a process of trial and error.

Although rare, some people do notice side effects from taking thyroid hormone replacement. Some women, for instance, may notice changes in their menstrual periods. Occasionally, people may have an allergic reaction to the dyes in thyroid medications. Other possible side effects include:

  • Weight loss

  • Diarrhea

  • Fever

  • Hair loss

  • Headache

  • Irritability

  • Leg cramps

  • Nausea and vomiting

  • Tremors

  • Insomnia

  • Such side effects are a nuisance but are not considered serious unless they persist. If you experience chest pain or an irregular heartbeat, however, you should contact your doctor immediately. Other side effects that warrant immediate medical attention include difficulty breathing; excessive sweating; or swelling in the ankles, feet, and legs.


    Most women are told to steer clear of medications while pregnant. Though this is generally a good idea, you should always continue to take your thyroid hormone replacement. Not only is the medication safe, but your body will need it to supply the growing fetus with thyroid hormone. The best thing to do is to tell your doctor ahead of time if you are trying to conceive and to let her know as soon as you do get pregnant. Your doctor may want to increase your dosage.

    In people who take drugs that contain T3, the side effects are the same. Too much T3 can cause anxiety, insomnia, and a rapid heartbeat. The side effects may be most apparent shortly after you take T3, when your body gets its first jolt of the hormone.

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